Article

The Effect of Operational Parameters on the Photocatalytic Degradation of Three Azo Dyes in Aqueous TiO2 Suspensions

May 2005
Journal of Photochemistry and Photobiology A Chemistry 172(1):89-96

DOI:10.1016/j.jphotochem.2004.11.009

Authors:

University of Isfahan

Photocatalytic degradation of three commercial textile diazo dyes, called (C.I. Direct 80, 3BL, C.I. Direct Blue 160, RL and C.I. Reactive Yellow 2, X6G) were investigated using commercial TiO2 in aqueous solution under 400 W high-pressure mercury lamp irradiation. The effect of oxygen, temperature, catalyst loading, UV-light irradiation time, solution pH and inorganic ions such as SO42−, Cl− and NO3− were studied and optimized values were obtained. Results show that the employment of efficient photocatalyst and selection of optimal operational parameters may lead to complete decolorization and to substantial decrease of the chemical oxygen demand (COD) of dye solutions.

BiOI-MIL Binary Composite for Synergistic Azo Dye AR14 Discoloration

Article

Full-text available

Jan 2025

Acid red 14 (AR14) is a widely used azo dye that belongs to a major family of commercial dyes employed extensively in the textile industry. The present study aimed to investigate the photocatalytic discoloration of AR14 using a visible-light-responsive catalyst. The composite catalyst was synthesized by integrating thermally modified MIL-101 (M-MIL) integrated into bismuth oxide. Thermal modification of MIL-101 produced octahedral α-Fe2O3 particles with a size of 1–2 μm, which were incorporated into bismuth oxyiodide (BiOI) featuring a nanosheet structure. BiOI@M-MIL composite exhibited an enhanced photocatalytic activity. The bandgap energy, Eg, of BiOI was reduced from 1.95 eV to 1.73 eV in the composite. Photocatalytic reactions were performed under visible-light irradiation using a 5 W cold LED lamp. The AR14 discoloration tests demonstrated that BiOI@M-MIL was 1.81-fold more efficient compared to pristine BiOI. Key parameters affecting AR14 discoloration —such as catalyst dosage, pH, dye concentration, and contact time, were investigated. The composite achieved almost a complete dye removal efficiency of 94.26% under experimental conditions. Radical trapping tests highlighted the crucial role of superoxide radicals, O2.−, in the dye discoloration process. BiOI@M-MIL takes advantage of simultaneous adsorption and photocatalysis with the highest adsorption capacity of 45.32 mg g−1 and 32.2 mg g−1, based on Sips and Langmuir models, respectively. The catalyst also showed good reusability and ~14% loss in removal efficiency after five consecutive cycles. In conclusion, the BiOI@M-MIL composite demonstrates excellent photocatalytic performance, combining low energy consumption with material stability, making it a promising candidate for AR14 discoloration.

Activation of Peroxymonosulfate by UV-254 nm Radiation for the Degradation of Crystal Violet

Article

Full-text available

Oct 2022

Water is a precious natural resource. Unfortunately, bodies of water become polluted by waste, such as untreated wastewater and detritus, along with oil spills, with minimum or no consideration for their limited capacity to renew themselves. Among these pollutants, dyes are harmful as they are persistent and not biodegradable in nature. The present study demonstrates the removal of crystal violet (CV), a toxic cationic dye, by using three systems: Peroxymonosulfate (PMS), UV-254 nm radiation and UV/P5MS. The effects of various parameters, such as the effects of the initial dose of crystal violet, initial concentration of PMS, pH, typical inorganic ions, etc., were also investigated. The effect of pH was investigated in the range of 1.92–12.07. Similarly, the effect of various anions such as NO2•−, HCO3•−, CO3•2−, SO4•2− and CH3COO•− was investigated for the degradation of target pollutants. The order of degradation of crystal violet was UV/PMS > PMS > UV with removal efficiencies of 97%, 76% and 42%, respectively, at reaction times of 60 min. The degradation of crystal violet was enhanced significantly at a pH range of 10.52–12.07. Electrical energy per order (EE/O) values for UV/PMS, PMS and UV were calculated to be 1.68, 3.62 and 48.96 KWh/m3/order, respectively. The addition of inorganic ions inhibited the removal of CV in the order of SO4•2− > NO2•− > HCO3•− > CO3•2− > CH3COO•−. Moreover, the kinetic studies on the degradation of CV by the UV-254 nm, PMS, and UV/PMS systems, were also carried out and found to follow pseudo-first-order kinetics. The study revealed that oxidation processes are most efficacious for the removal of organic dyes from wastewater.

Degradation of dye in a continuous zig-zag flow pattern photocatalytic reactor using a Doehlert matrix

Article

Sep 2022
CHEM ENG RES DES

Rhodamine B-containing wastewater was thoroughly treated in a photocatalytic reactor operated in a continuous mode with a zig-zag type of flow pattern. The effect of operating parameters such as pH (1–9) and initial dye concentration (10–40 ppm) on Rhodamine B degradation was studied at 1 g/L of TiO2 and H2O2 in order to determine the optimal operating parameters for combined treatment schemes. At a concentration of 10 ppm and a loading of 1 g/L TiO2 and H2O2 at a pH of 3, the maximum rate of degradation was 94.02%, and 96.68% obtained and follows pseudo-first order kinetics, respectively. Further studies of the influence of initial dye concentration and solution pH were investigated using an optimized range of TiO2 and H2O2 loading based on the surface response of the Doehlert matrix design. Based on the surface response, it was observed that the lower initial concentration with a higher loading of TiO2 and H2O2 accelerates the production of hydroxyl radicals and thereby, higher degradation of pollutants was achieved. Complete degradation with 84.76% COD reduction of Rhodamine B was observed at 0.8 g/L of H2O2 and 2 pH of dye solution with a total treatment cost of US $0.009/L. Overall, the current study found that the novel photocatalytic reactor operated in a continuous mode can treat large volumes of waste water using hybrid methods with optimum catalyst loading, has high potential, and may be successfully applied for the removal of hazardous dyes from aqueous solutions with intensification benefits.

Phase separation, binding nature, and physico-chemical variables of TX-100 + crystal violet mixture: effects of the electrolytes and hydrotropes

Article

Full-text available

Mar 2025
COLLOID POLYM SCI

This study has explored the potential interactions between Triton X-100 (TX-100) and crystal violet dye (CV) in the presence of different electrolytes and hydrotrope (HDT) solutions by using cloud point (CP) measurement and UV–visible spectroscopic techniques. The studied electrolytes are sodium chloride (NaCl), sodium acetate (NaOAc), and sodium sulfate (Na2SO4), whereas the HDTs are sodium salicylate (NaSal), sodium benzoate (NaBenz), and 4-amino benzoic acid (4-ABA). There was a sharp increase in the CP values of the system studied in NaSal and NaBenz media due to “salting-in” effect, whereas the lowering in the magnitudes of CP was recorded in aqueous solutions of NaCl, NaOAc, Na2SO4, and 4-ABA as a result of “salting-out” effect. The extents of CP in the experimental system were varied with the enhancement of different electrolytes and HDTs concentration which followed the trend as

\normalsize {\text{CP}}_{\text{aq. NaSal}}>{\text{CP}}_{\text{aq. NaBenz}}>{\text{CP}}_{\text{aq. NaOAc}}>{\text{CP}}_{\text{aq. NaCl}}>{\text{CP}}_{{\text{aq. Na}}_{2}{\text{SO}}_{4}}>{\text{CP}}_{aq.4-\text{ABA}}

. The binding constant (

{K}_{b}

) for the complexation of CV and TX-100 was determined by using the Benesi–Hildebrand equation with the help of UV–Vis spectroscopic method. The degree of

{K}_{b}

was found to be dependent on the presence of salts and variation in temperatures. The recorded

{\Delta G}_{c}^{0}

and

{\Delta G}_{b}^{0}

values for the phase segregation and binding were found as positive and negative, respectively, in all experimental cases. The positive magnitudes of

{\Delta G}_{c}^{0}

showed a decreasing trend by the boost of electrolytes and HDT concentrations. The appearances of

-{\Delta H}_{c}^{0}

and

{-\Delta S}_{c}^{0}

values in the solutions of different electrolytes confirmed the H-bonding and dipole–dipole interactions being in function amid the surfactant/dye mixtures in the aqueous media, whereas

+{\Delta H}_{c}^{0}

and

+{\Delta S}_{c}^{0}

values found in aq. NaSal and aq. NaBenz media were indicative of hydrophobic interactions to be have occurred between TX-100 and CV dye species. Both

{\Delta H}_{b}^{0}

and

{\Delta S}_{b}^{0}

values of binding were found to be positive revealing the presence of ion–dipole and hydrophobic interactions which were responsible for the binding of the respective components within the experimental surfactant–dye system. These significant results will be of great resource of knowledge to the researchers in the respective fields as well as highly useful for the formulations of quality products in various textiles and pharmaceutical industries. Graphical Abstract

Comprehensive Investigation of Perovskite Materials for Photocatalytic, Photovoltaic, and Optoelectronic Applications: Recent and Advance Challenges and Goals

Article

Full-text available

Aug 2024

Energy and environment are two of the most important issues of our time on a worldwide scale. Photocatalysis is the most environmentally friendly answer to these issues. Perovskite-based materials have sparked attention due to their low cost and lack of toxicity. Substitutable solar energy and semiconductor photocatalytic technologies are two of the most essential ways to reduce or avert global catastrophes and energy concerns. It is estimated that over one thousand different materials such as KGaO3 and RbMg2Ti3O10 have been tested for their potential as photocatalysts recently. Among the many endeavors, the production of photocatalysts is seen as a crucial technique for using solar energy for long-term energy and environmental reasons. Many photocatalysts (RbGaO3) have previously been combined. A photoelectrochemical cell is a device that converts light to electricity via a photoelectrochemical reaction. The sun is the major source of our power. Clean hydrogen energy is generated by a photocatalyst, which removes both inorganic and organic contaminants from water. Photocatalysts that operate over the whole solar spectrum have been developed as a result of significant advances in this area. Among the various materials that have been produced so far, single- and double-perovskite-based materials have received a lot of attention.

Enhanced light absorption and charge carrier’s separation in g-C3N4-based double Z-scheme heterostructure photocatalyst for efficient degradation of navy-blue dye

Article

Full-text available

Jul 2024

Effective wastewater treatment is essential due to the dye environmental threats. Photocatalysis offers an eco-friendly dye degradation solution. Herein, we report a double Z-scheme photocatalyst, i.e. LaFeO3/Boron-doped g-C3N4/Fe2O3 (LFO/B-CN/FO), fabricated via a hydrothermal method. The formation of this ternary system is supported by structural, surface, and morphological analyses. Differential scanning calorimetry and thermal gravimetric analysis demonstrated the crystallization behavior of the composite. Because of synergetic effects in the ternary composite and boron doping, the optical band gap energy is reduced to 1.6 eV. Under visible light irradiation, the LFO/B-CN/FO nanocomposite degraded navy-blue dye by 98% in 130 min at neutral pH, surpassing CN, B-CN, and binary composites of B-CN with LFO and FO. The degradation process was rationalized using pseudo-first- and pseudo-second-order kinetic models, which confirmed high catalytic efficiency. The double Z-scheme heterojunction enhanced light absorption, charge separation, and carrier lifetime, hence improving the photocatalytic activity. Overall, the as-fabricated LFO/B-CN/FO ternary composite outperformed reference catalysts in terms of chemical reactivity, optical characteristics, and electrical performance. This work opens up a new route for the design and fabrication of double Z-scheme ternary composite photocatalysts for potential wastewater treatment and renewable energy applications.

Performance and hydrodynamic study of a new multi‐stage solar photoreactor with immobilized ZnO for synthetic wastewater treatment

Article

Full-text available

Jun 2024
ENVIRON PROG SUSTAIN

This study aims to design a new multi‐stage photoreactor with immobilized ZnO and assess its performance in reducing textile wastewater toxicity using solar energy. The electric conductivity measurement is retained as a detection method to obtain the residence time distribution (RTD) function. The RTD is then used to characterize the hydrodynamic behavior of the photoreactor and to evaluate its deviation from the distribution curves of ideal reactors. Solar experiments are conducted to demonstrate the performance of this multistage reactor towards the degradation of a textile azo dye namely Solophenyl Red 3BL (SR 3BL). The influence of the flow rate and the SR 3BL initial concentration (CO) are considered. The variation of the flow rate slightly influences the SR 3BL photodegradation efficiency and it is inversely proportional to its concentration. The study of the reuse of the immobilized catalyst shows that the degradation efficiency of 98% is reached even after multiple photocatalytic cycles. The figure of merit collector area per order was in the range of 35 to 110 m2/m3order. This result provides useful information for scaling up and estimating energy efficiency of the reactor.

Green synthesis of ZnFe2O4@BC nanocrystals using pomelo peel waste for photo‐Fenton degradation of dye under visible light

Article

Full-text available

Mar 2024

In this study, an economical ZnFe2O4@BC composite was successfully synthesized using pomelo peel biochar through a simple one‐pot thermal‐calcination roasting method. The combination of biochar and ZnFe2O4 was confirmed by FTIR, XRD, Raman, TEM, and XPS analysis, confirming that the successful insertion of carbon into the oxygen sites of the ZnFe2O4 lattice, forming C−O bonds. The incorporation of biochar resulted in a high specific surface area, providing more active sites for catalytic reactions, enhancing electron transport, effectively separating electron‐hole pairs, increasing light capturing capacity, and restraining the leaching of metals. The Zn vacancy acted as an electron acceptor, promoting electron transfer in the catalyst by reducing the lowest unoccupied orbital position. Additionally, various reaction parameters such as solution pH, iron content, catalyst dosage, and H2O2 volume were investigated to elucidate their effects on the degradation performance. This study proposes a novel method for synthesizing carbon‐coated metal oxide semiconductors, which shows great potential for environmental and energy‐related applications.

A Facile Surfactant-assisted Synthesis of Graphene Oxide/Zinc Oxide Catalyst for the Degradation of Methylene Blue Dye

Article

Full-text available

Feb 2024
WATER AIR SOIL POLL

In this work, electrochemically exfoliated graphene oxide-based photocatalyst was synthesised with the help of single- (sodium dodecyl sulphate; SDS) and triple-chain (sodium 1,4-bis(neopentyloxy)-3-(neopentylcarbonyl)-1,4-dioxobutane-2-sulfonate; TC14) anionic surfactants. The hybrid photocatalyst is a system consisting of surfactant-assisted electrochemically exfoliated graphene oxide (sEGO) and zinc oxide (ZnO). The system was prepared by exfoliating graphite in the presence of surfactant and ZnO, and it was used for the removal of methylene blue (MB) dye. Of these different surfactants, the triple-chain TC14 exhibited 98.53% MB removal, which was significantly higher than the system with SDS surfactant (50.94%) or ZnO alone (42.33%). Observations through field-emission scanning electron microscopy suggested an enhanced exfoliation degree upon increasing the number of surfactant chains. Results from zeta potential measurement also revealed increased system stability along with a high number of surfactant chains and the addition of ZnO into the system. These findings highlight the importance of tailoring the surfactant’s chemical structure to achieve enhanced graphene oxide-based photocatalyst performance for MB dye removal and wastewater treatment.

CINETIC STUDY OF PHOTOCATALYTIC DEGRADATION BY THE (TiO2/UV) SYSTEM OF INDIGO CARMINE DYE IN AQUEOUS SOLUTION

Article

Full-text available

Dec 2023

The persistence of synthetic dyes in the environment and the ineffectiveness of most conventional depollution techniques have led the scientific community to turn to advanced oxidation processes for eliminating these dyes from water. The aim of this work was to experiment with heterogeneous photocatalysis in the degradation of indigo dye in aqueous solution. The catalyst used was titanium dioxide in the anatase PC 500 form, irradiated by a polychromatic ultraviolet lamp with a wavelength Î»= 365 nm. This technique proved effective, with a 77% degradation rate compared with photolysis, which removed only 17% of the indigo dye under the same conditions. Also, this work showed that low-concentration solutions were easily degraded with total decolourisation of the 12 mg/L molecule after 4 hours compared with 80% elimination of the 32 mg/L solution.The study of the influence of light intensity showed an increase in the rate of degradation of the molecule when the number of lamps placed in the reactor was increased. Total degradation was observed when 4 lamps were used for 120 minutes of irradiation.

Dyes Degradation with Fe-Doped Titanium Nanotube Photocatalysts Prepared from Spend Steel Slag

Article

Full-text available

Apr 2013
INT J PHOTOENERGY

TiO 2 has been studied most commonly because it has high stability, nontoxicity, high catalytic activity, and high conductivity. Many studies have shown that TiO 2 would generate electron-hole pairs illuminated with UV and surround more energy than that before being illuminated. In this study, the titanium nanotube (TNT) photocatalysts were prepared to increase the surface area and adsorption capacity. The Fe TNT was also prepared from a slag iron since many slag irons cause waste treatment problems. In this study, a different Fe loading was also assessed since TNT doped with metals can be used to improve the degradation efficiency. Furthermore, five kinds of dye concentration, including 10, 20, 100, 200, and 400 ppm, and five kinds of Fe-doped content, including 0, 0.77, 1.13, 2.24, and 4.50%, were tested. Different kinds of reaction time and dye species were also assessed. In this result, Direct Black 22 was the most difficult to be degraded, although the concentration was decreased or the dose amount was increased. The degradation efficiency of 10 ppm Direct Black 22 was below 40% with 0.04 gL −1 TNT under 365 nm UV irradiation.

Petroleum Refinery Wastewater Treatment using a Novel Combined Electro-Fenton and Photocatalytic Process

Article

Full-text available

Sep 2023
J IND ENG CHEM

In the current study, treatment of petroleum refinery wastewater has been successfully achieved using a novel photocatalysis-ElectroFenton system operated at a batch circulation mode and composed from a tubular electro-Fenton reactor provided with a macro-porous graphite air diffusion cathode (MPGADC) combined with a new configuration of photo reactor. The feasibility of the combined electro-Fenton with photo-catalytic process (EF + UV/ TiO2) was evaluated using response surface methodology (RSM) with Box-Behnken design (BBD). Titanium dioxide (Anatase) was used as a photo-catalyst and characterized by x-ray diffractometer (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spec- troscopy (FTIR), and Brunauer–Emmett–Teller surface area (BET). Four main operating variables were studied: current density (5–15 mA/cm2, Fe2+concentration (0.1–0.5 mM), TiO2 dosage (0.1–0.7 g/l), and reaction time (20–60 min). Results revealed that reaction time has the most effective parameter on the EF + UV/ TiO2 process followed by TiO2 dosage, Fe2+concentration, and current density. The optimum operating conditions for maximizing COD removal (RE%) and minimizing the total electrical energy con- sumption (EECT)) were found to be a current density of 15 mA/cm2, Fe2+ concentration of 0.5 mM, TiO2 dosage of 0.7 g/l, and a reaction time of 54 min in which COD removal of 91.26 % was achieved with claiming EECT of 26.86 kWh/m3. Results revealed a vital improvement of using EF + UV/ TiO2 in compar- ison with UV/ TiO2 alone where an enhancement of 23% in RE% and a reduction by 55% of EECT were observed. Furthermore, a kinetic study was performed for EF + UV/TiO2 and UV/ TiO2 alone in which the results revealed that decay of COD obeyed a pseudo-first-order kinetic for the two processes with a high-rate constant for EF + UV/ TiO2 process.

Recent Advances in the Photocatalytic Degradation of Direct Blue Dyes: A Critical Minireview and Analysis Study Mini Review

Article

Full-text available

Jan 2021

Different dyes are used in numerous industries, including food, paper, ink, and the textile industry. Among various dye types, Direct Dyes have great significance because of their properties and applications. Such applications are paper, cotton, leather, and cellulose. The textile industry is considered a main contributor to the water pollution problem because it releases large quantities of coloured liquid waste. The majority of dyes and their products are considered carcinogenic, toxic, and resistant compounds. Therefore, the application of common wastewater treatments is not sufficient for dye removal such as adsorption, biological and chemical degradation. The advanced oxidation process using photocatalytic oxidation is an effective technique that can mineralize complicated aromatics and different organic dyes among various treatment methods. In this review, the photocatalytic degradation of Direct Blue dyes is discussed. The review is mainly focused on the recent advances in the photocatalysts and their activity improvement using different dopants.

Dyes Degradation with Fe-Doped Titanium Nanotube Photocatalysts Prepared from Spend Steel Slag

Article

Full-text available

Apr 2013
INT J PHOTOENERGY

Rapid Removal of Organic Pollutants from Aqueous Systems under Solar Irradiation Using ZrO2/Fe3O4 Nanoparticles

Article

Full-text available

Nov 2022
MOLECULES

Pure water scarcity is an emerging, all-around problem that globally affects both the life quality and the world’s economy. Heterogeneous photocatalysis under solar irradiation is a promising technique for the organic pollutants (e.g., pesticides, drugs) removal from an aqueous environment. Furthermore, the drawbacks of commercially available photocatalysts can be successfully overcome by using innovative nanoparticles, such as ZrO2/Fe3O4. Four ZrO2/Fe3O4 nanopowders with a different mass ratio of ZrO2 and Fe3O4 were synthesized using the chemical co-precipitation method. XRD analysis showed the presence of magnetite and hematite Fe-oxide phases in all samples. The content of the magnetite phase increased with the addition of 19% ZrO2. The efficiency of the newly synthesized ZrO2/Fe3O4 nanoparticles was investigated in the rapid removal of selected pollutants under various experimental conditions. Nevertheless, the influence of the water matrix on photocatalytic degradation was also examined. The obtained data showed that using ZrO2/Fe3O4 nanosystems, an appropriate removal rate of the selected pesticides and pharmaceuticals can be reached after 120 min of solar irradiation. Further, the total organic carbon measurements proved the mineralization of the target emerging pollutants. ZrO2/Fe3O4 nanoparticles are economically feasible, as their removal from the suspension can be easily achieved using affordable, environmentally-friendly magnetic separation.

Photocatalytic Degradation of Methylene Blue Dye under Solar Irradiation Using TiO2-Based Nanocomposites

Preprint

May 2022

Afrina Zaman Shoronika

Removal of methylene blue pollutant from the textile industry by adsorption onto Zeolithe: Kinetic and thermodynamic study

Article

Full-text available

Sep 2022
J ENG FIBER FABR

Moussa Abbas

In the textile industry, various acidic, basic and reactive dyes are used for different applications; the aim of this study is to eliminate Methylene blue (MB) a dangerous dye by a zeolithe produced at low economic cost by adsorption in batch mode. The adsorbent was characterized by the FTIR spectroscopy, X-ray diffraction (XRD), and point of zero charge (pHpzc = 10.42). Some examined factors were found to have a significant impact on the adsorption capacity of the zeolithe like the initial dye concentration (5–25 mg/L), solution pH (2–14), adsorbent dose (0.1–2 g/L), agitation speed (150–500 rpm), particles size (100–500 µm) and temperature (298–333 K). The best capacity was found at pH 6 with an adsorbent dose 0.2 g/L, an agitation speed 200 rpm and a contact time of 40 min. Modeling the Kinetics and Isotherms data shows respectively that the pseudo-second-order kinetic model and Langmuir isotherm provide better fitness to the experimental data with the maximum adsorption capacity of 12.50 mg/g at 25°C. The adsorption isotherms at different temperatures have been used for the determination of the free energy (ΔG°); enthalpy (ΔH°) and entropy (ΔS°) to predict the nature of MB adsorption. The positive values of ΔG° and ΔH° indicate a non-spontaneous and endothermic MB adsorption with a physisorption process. The adsorbent elaborated from the zeolithe was found to efficient and suitable for the removal of reactive dyes from aqueous solutions, due to its, low cost preparation and good adsorption capacity. The photocatalysis of MB in the presence of hybrid semiconductor (TiO 2 /Zeolithe) constitutes the logical continuation of this study.

Treatment of oily wastewater using photocatalytic membrane reactors: A critical review

Article

Sep 2022

Oily wastewater is generated from various sources such as oil/gas exploration (produced water), oil refining, pharmaceutical, food industries, and household waste. Toxins in oily wastewater often percolate into drinking water, seawater, and groundwater. This becomes a source of environmental and public health concern. Due to its hazardous nature, the discharge of oily wastewater into the environment is strictly regulated. This work critically reviews progress in photocatalytic membrane reactor (PMR) for oily wastewater treatment, regulations on allowable oil discharge, various factors that affect PMR performance, and its self-cleaning and anti-fouling properties in oily wastewater treatment. Their removal performance for stabilized oil emulsion and trace oil contaminants is highlighted. This work also evaluates trends of integrated techniques, utilization of functional materials, PMR scale-up and the outlook of PMR. It was evident from 226 published articles (1976-2022) that oily waste water contamination has been a source of concern and PMR which integrates both membrane filtration and photodegradation processes, has emerged as a promising technology for oily wastewater, simultaneously degrading oil emulsion and undertaking filtration. The PMRs attained over 96% oil rejection. Both the UV and visible light aided the degradation of oil using the PMR. High membrane surface area, provides additional sites for the photocatalyst to occupy, contributing to an efficient degradation. Concludingly, PMRs can exhibit a high flux of recovery ratio after several filtration cycles under UV Vis irradiation, and with proper design and fabrication methods, the membranes can do self-cleaning and be re-used for several cycles of filtration with high efficiency.

Application of response surface methodology for methylene blue removal using an innovative ZIF-8/NiFe2O4/ halogen lamp system

Preprint

Full-text available

Aug 2022

In this present research, magnetic nanoparticles of ZIF-8/NiFe 2 O 4 were synthesized using a green and simple method to photodegrade methylene blue in presence of visible-light irradiation. The structures and morphologies properties of the as-synthesized nanoparticles were characterized by XRD, FTIR, SEM, TEM, and PL for individual ZIF-8, NiFe 2 O 4 , and ZIF-8/NiFe 2 O 4 materials. Response surface method (RSM) by considering the central composite design (CCD) was used to design the experiments and optimize the process. The F-value (248.26) and p-value < 0.0001 imply that the model is significant. The obtained RSM model with R ² = 0.996 showed a satisfactory correlation between the predicted values and experimental results of MB removal. The maximum decolorization efficiency of MB was obtained under the optimum experimental conditions of 0.044 g/100mL catalyst dose, 5 mg/L initial dye concentration, 150 min irradiation time, and dye solution pH of 7.4.

Biosynthesis of highly porous Ag/Bi/SnO2 nanohybrid material using seeds extract of Caesalpinia bonduc and their photocatalytic activity

Article

Aug 2022
PHYSICA B

In the current study, Tin oxide (SnO2), Silver–Tin oxide (Ag–SnO2), and Ag–Bi–SnO2 nanoparticles (NPs) were successfully synthesized using methanolic seed extracts of Caesalpinia bonduc (C.bonduc) plants. The NPS were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Surface area analysis (SAA), energy dispersive X-ray (EDX) analysis, and Fourier transmission infrared (FTIR). The synthesized photocatalyst's surface area was 210, 235, and 238 m²/g for SnO2 and Ag–SnO2, and Ag–Bi–SnO2, respectively. The catalyst showed excellent activity for the degradation of MB dye in an aqueous medium. The results confirmed that the Ag–Bi–SnO2 exhibited 94% degradation of dye compared to Ag–SnO2 (90%) and SnO2(80%) under the same reaction conditions. Adding Ag and bismuth can also increase the degradation mechanism by preventing recombining electron-hole pairs. The report is novel, as no report to date has been published for the synthesis of Ag–Bi–SnO2, Ag–SnO2, and SnO2 NPs synthesized by C. bonduc seed extract; the procedure is simple, cheaper, and non-toxic compared to other methods employed for the synthesis of NPs. Eley-Rideal (ER) type of reaction mechanism was found to follow the degradation of MB dye in an aqueous medium.

Removal and recovery of aqueous U(VI) by heterogeneous photocatalysis: Progress and challenges

Article

Aug 2022
CHEM ENG J

With the rapidly expanding implementations of nuclear power technology, the contamination of the aquatic environment by uranium is a rising environmental problem. Photocatalytic reduction of hexavalent uranium (U(VI)) is a plausible solution to the aqueous uranium contamination, which has generated increasing research interest in the recent decade. Therefore, a systematic assessment highlighting the important direction for future studies is in need. We herein present a critical review to address the following two aspects: (1) the progress and current understandings of photocatalytic U(VI) removal technology, including various applied catalysts, current understanding of the kinetics and mechanisms, the effects of key operation parameters, and the effects of co-existing water constituents; (2) key knowledge gaps that need future research efforts in this field.

Catalytic reduction of hazardous acid orange 10 dye by BiVO4/TiO2 nanocrystalline heterojunction and influence of aeration, FeSO4, H2O2 and FeCl3 on removal efficiency: A novel and environmentally friendly process

Article

Full-text available

May 2022

Bismuth vanadate in combination with titanium dioxide were synthesized by hydrothermal method and its photocatalytic activity was investigated under visible light irradiation for acid orange 10 (AO10) dye removal. The 10% BiVO4/TiO2 showed the highest catalytic activity in comparison with 20, 30, 40 and 50% BiVO4/TiO2 ratios. The removal of AO10 azo dye in aqueous solutions was studied in laboratory-scale experiments using 25 removal processes and their removal efficiencieswere evaluated, separately. The results showed that the amount of de-colorization for each oxidation process is completely different. The order of the investigated processes in removing the dye after 90 min is as follows: LED < TiO2 < BiVO4 < 10% BT/without LED < BiVO4/ LED < 50% BT < 40% BT < 30% BT < 20% BT < UV/H2O2 < 10% BT < 5a-10%BT < 5F-10%BT < 10a-10%BT < 50F-10%BT < 20a-10%BT < 10F-10%BT < 20F-10%BT < 20H-10%BT < 40H-10%BT < 50H-10%BT < 20a-20F-10%BT < 20a-20F-50H-10%BT. Among the above processes, 20a-20F-50H-10%BT had the best removal performance and can be suggested for using in real conditions. Coagulation/precipitation process was done using 5 mg/L of FeCl3 as post-treatment reaching efficiency of 100% in the studied system.

SnO2/UV/H2O2 and TiO2/UV/H2O2 Efficiency for the Degradation of Reactive Yellow 160A: By-Product Distribution, Cytotoxicity and Mutagenicity Evaluation

Article

Full-text available

May 2022

Advanced oxidation processes (AOPs) have emerged as a promising approach for the removal of organic dyes from effluents. Different AOPs were employed for the degradation of Reactive Yellow 160A (RY-160A) dye, i.e., SnO2/UV/H2O2 and TiO2/UV/H2O2. In the case of UV treatment, maximum degradation of 28% was observed, while UV/H2O2 furnished 77.78% degradation, and UV/H2O2/TiO2 degraded the RY-160A dye up to 90.40% (RY-160A 30 mg/L, 0.8 mL of H2O2). The dye degradation was 82.66% in the case of UV/H2O2/SnO2 at pH 3. FTIR and LC-MS analyses were performed in order to monitor the degradation by-products. The cytotoxicity and mutagenicity of RY-160A dye were evaluated by hemolytic and Ames (TA98 and TA100 strains) assays. It was observed that the RY-160A dye solution was toxic before treatment, and toxicity was reduced significantly after treatment. Results indicated that UV/H2O2/TiO2 is more efficient at degrading RY-160A versus other AOPs, which have potential application for the remediation of dyes in textile effluents.

Green synthesis of microalgae-based carbon dots for decoration of TiO2 nanoparticles in enhancement of organic dye photodegradation

Article

Dec 2021
ENVIRON RES

TiO2 is a well-known semiconductor used widely in the photocatalyst field, but its photocatalytic applications are hampered by a fast electron–hole recombination rate and low visible light absorption due to a wide-band-gap energy. Herein, we present a simple, low cost, and green approach to obtain carbon dots from microalgae, namely microalgae-based carbon dots (MCDs), using an unprecedented microwave-assisted treatment. The MCDs were successfully decorated on the surface of TiO2 nanoparticles. The as-prepared composite exhibited a superior photodegradation of methylene blue, compared with pristine TiO2 (83% and 27%, respectively) under visible light irradiation. The MCDs in TiO2-MCDs serve as electron reservoirs to trap photoinduced electrons and as photosensitizers for the improvement of visible light absorption; both factors play an important role in the improvement of the TiO2 photocatalytic activity. Furthermore, the as-prepared composite photocatalyst also exhibits high photostability and recyclability during the photodegradation of methylene blue. Therefore, this work provides an original approach to the development of environmentally friendly and highly effective photocatalysts for the treatment of various organic pollutants, which can go a long way toward ensuring a safe and sustainable environment.

Investigation of environmental and therapeutic applications of holmium doped titanium dioxide (Ho-TiO2) nanocatalysts. Kinetic and thermodynamic study of the photocatalytic degradation of Safranin O dye

Article

Full-text available

Dec 2021

Titanium dioxide (TiO2) and Holmium doped Titanium dioxide(Ho-TiO2) nanoparticles (NPs) were synthesized through Sol Gel method. The synthesized NPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDX), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Photoluminescence spectroscopy. DNA binding, antibacterial, hemolytic and antioxidant assays of the synthesized nanoparticles were also carried out for finding their therapeutic applications. Successful doping of TiO2 with Ho reduced the band gap from 3.10 to 2.88 eV. SEM and XRD analysis showed that both TiO2 and Ho-TiO2 NPs exhibit tetragonal structure and as a result of doping the morphology of the particles improved and agglomeration reduced. PL emission intensity of TiO2 also reduced with doping.The holmium doped TiO2 were used for the first time against the degradation of Safranin O dye, DNA binding study and biocompatibility assay.The degradation of Safranin O dye over both the catalysts followed first order kinetics. The calculated activation energies for the photo degradation of given dye were found to be 51.7 and 35.2 kJ/mol using TiO2 and Ho-TiO2 NPs respectively. At 180 minutes time interval 84 and 87% dye degradation was observed using pure TiO2 and Ho-TiO2 NPs respectively. High percent degradation of dye was found at low concentration (20 ppm) and at optimal dosage (0.035 g) of both the catalysts. The rate of Safranin O dye degradation was found to increase with increase in temperature and pH of the medium. DNA binding study revealed that Ho-TiO2 NPs are more capable of binding to human DNA. Antibacterial activity study showed that Ho-TiO2 NPs were more efficient against both gram-negative and gram-positive bacterial strains as compared to pure TiO2. Hemolysis assay showed that TiO2 and Ho-TiO2 nanoparticles are non-biocompatible.Ho-TiO2 nanoparticles showed higher anti-oxidant activity as compared to bare TiO2.

Investigation of Environmental and Therapeutic Applications of Holmium doped Titanium dioxide (Ho-TiO2) nanocatalysts. Kinetic and Thermodynamic study of the Photocatalytic degradation of Safranin O dye

Article

Full-text available

Feb 2022

Titanium dioxide (TiO2) and Holmium doped Titanium dioxide(Ho-TiO2) nanoparticles (NPs) were synthesized through Sol Gel method. The synthesized NPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis (EDX), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Photoluminescence spectroscopy. DNA binding, antibacterial, hemolytic and antioxidant assays of the synthesized nanoparticles were also carried out for finding their therapeutic applications. Successful doping of TiO2 with Ho reduced the band gap from 3.10 to 2.88 eV. SEM and XRD analysis showed that both TiO2 and Ho-TiO2 NPs exhibit tetragonal structure and as a result of doping the morphology of the particles improved and agglomeration reduced. PL emission intensity of TiO2 also reduced with doping.The holmium doped TiO2 were used for the first time against the degradation of safranin O dye, DNA binding study and biocompatibility assay.The degradation of Safranin Odye over both the catalysts followed first order kinetics. The calculated activation energies for the photo degradation of given dye were found to be 51.7 and 35.2kJ/mol using TiO2 and Ho-TiO2 NPs respectively. At 180 minutes time interval 84% and 87 % dye degradation was observed using pure TiO2 and Ho-TiO2 NPs respectively. High percent degradation of dye was found at low concentration (20ppm) and at optimal dosage (0.035g) of both the catalysts. The rate of Safranin O dye degradation was found to increase with increase in temperature and pH of the medium. DNA binding study revealed that Ho-TiO2 NPs are more capable of binding to human DNA. Antibacterial activity study showed that Ho-TiO2 NPs were more efficient against both gram-negative and gram-positive bacterial strains as compared to pure TiO2. Hemolysis assay showed that TiO2 and Ho-TiO2 nanoparticles are non-biocompatible.Ho-TiO2 nanoparticles showed higher anti-oxidant activity as compared to bare TiO2.

A novel Sm doped Cr2O3 sesquioxide-decorated MWCNTs heterostructured Fenton-like with sonophotocatalytic activities under visible light irradiation

Article

Nov 2021
J HAZARD MATER

Novel Sm doped Cr2O3 decorated MWCNTs nanocomposite photocatalyst was successfully prepared by a facile hydrothermal method for metoprolol (MET) degradation. A heterogeneous photo -Fenton like system was formed with the addition of H2O2 for ultrasonic irradiation (US), visible light irradiation (Vis) and dual irradiation (US/Vis) systems. The intrinsic characteristics of Sm doped Cr2O3 decorated MWCNTs nanocomposite was comprehensively performed using state-of-art characterization tools. Optical studies confirmed that Sm doping shifted the absorbance of Cr2O3 towards the visible-light region, further enhanced by MWCNTs incorporation. In this study, degradation of metoprolol (MET) was investigated in the presence of Cr2O3 nanoparticles, Sm doped Cr2O3 and Sm doped Cr2O3 decorated MWCNTs nanocomposites using sonocatalysis and photocatalysis and simultaneously. Several different experimental parameters, including irradiation time, H2O2 concentration, catalyst amount, initial concentration, and pH value, were optimized. The remarkably enhanced sonophotocatalytic activity of Sm doped Cr2O3 decorated MWCNTs could be attributed to the more formation of reactive radicals and the excellent electronical property of Sm doping and MWCNTs. The rate constant of degradation using sonophotocatalytic system was even higher than the sum of rates of individual systems due to its synergistic performance based on the kinetic data. A plausible mechanism for the degradation of MET over Sm-Cr2O3/MWCNTs is also demonstrated by using active species scavenger studies and EPR spectroscopy. Our findings imply that (•OH), (h⁺) and (•O2⁻) were the reactive species responsible for the degradation of MET based on the special three-way Fenton-like mechanism and the dissociation of H2O2. The durability and stability of the nanocomposite were also performed, and the obtained results revealed that the catalysts can endure the harsh sonophotocatalytic conditions even after fifth cycles. Mineralization experiments using the optimized parameters were evaluated as well. The kinetics and the reaction mechanism with the possible reasons for the synergistic effect were presented. Identification of degraded intermediates also investigated.

Investigating the efficacy of Palladium Doped Ceria for the Photodegradation of Azo Dyes

Article

Oct 2024
J MOL STRUCT

Heterogeneous catalysis for the environment

Article

Jan 2024

Anthropogenic climate and environmental changes increasingly threaten the sustainability of life on Earth, hindering the sustainable development of human societies. These detrimental ecological changes are driven by human activities that have elevated atmospheric levels of greenhouse gases and toxic substances, increased inorganic and organic pollutants in water bodies, and led to the accumulation of solid waste in soils. Over the next two to three decades, the impacts of climate change, water pollution, and soil contamination are expected to intensify, posing increasing risks to human health and global stability. Considering these trends, it is essential to implement robust mitigation and adaptation strategies. This paper analyzes environmental pollution problems from the perspectives of atmospheric, water, and soil contamination. It summarizes current research on heterogeneous catalysis for treating pollutants in gaseous, liquid, and solid phases, with an emphasis on the key challenges of applying these catalytic conversion technologies in cost-effective industrial settings. Finally, strategies for mitigating environmental pollutants via heterogeneous catalysis are discussed from the perspectives of material flow, energy flow, and data flow. This paper aims to offer scientific insights to enhance future research and practice in heterogeneous catalysis for environmental remediation.

Enabling highly efficient navy-blue dye degradation over the LaFeO3/ B-g-C3N4/WO3 double z-scheme heterostructure

Article

Sep 2024
J ALLOY COMPD

Perovskite Nanocomposite: A Step Toward Photocatalytic Degradation of Organic Dyes

Article

Aug 2024

Metal halide perovskites offer a promising opportunity for transforming solar energy into chemical energy, thereby addressing pressing environmental challenges. While their excellent optoelectronic properties have been successfully applied in photovoltaics, their potential in photocatalysis remains relatively unexplored. Herein, we report a novel humidity‐driven approach for the in situ synthesis of MAPbI 3 nanocrystals (NCs) within a nickel acetate matrix, forming a nanocomposite thin film that enhances the system's stability and enables its use in photochemical reactions. UV‐Vis spectroscopy and X‐ray diffraction confirm the rapid and effective synthesis of NCs within the matrix after 1 min at 80% relative humidity (RH). Optimal photoconversion conditions are attained after 60 min of exposure at 80% RH, due to the increased porosity and nanocrystal size over time as revealed by electron microscopy. The MAPbI 3 ‐Ni(AcO) 2 nanocomposite exhibits superior photocatalytic activity compared to standard polycrystalline MAPbI 3 films for the decomposition of Sudan III under simulated sunlight. Furthermore, the nanocomposite demonstrates good recyclability over multiple cycles. Overall, this work highlights the potential of MHP‐based nanocomposites for solar‐driven catalytic systems in pollution mitigation.

Formulation of silver phosphate/graphene/silica nanocomposite for enhancing the photocatalytic degradation of trypan blue dye in aqueous solution

Article

Full-text available

Jul 2024

Photocatalytic degradation of several harmful organic compounds has been presented as a potential approach to detoxify water in recent decades. Trypan Blue (TB) is an acidic azo dye used to distinguish live cells from dead ones and it's classified as a carcinogenic dye. In this study, silver phosphate (Ag3PO4) nanoparticles and novel Ag3PO4/graphene/SiO2 nanocomposite have been successfully prepared via simple precipitation method. Afterward, their physical properties, chemical composition, and morphology have been characterized using SEM, EDS, TEM, SAED, BET, XRD, FTIR and UV–VIS spectroscopy. The specific surface area of Ag3PO4 and Ag3PO4/G/SiO2 nanocomposite were reported to be 1.53 and 84.97 m²/g, respectively. The band gap energy of Ag3PO4 and Ag3PO4/G/SiO2 nanocomposite was measured to be 2.4 and 2.307 eV, respectively. Photocatalytic degradation of Trypan blue (TB) was studied at different parameters such as pH, catalyst dosage, initial concentration, and contact time. The results showed that, at initial dye concentration of 20 ppm, pH = 2, and using 0.03 g of Ag3PO4/G/SiO2 as a photocatalyst, the degradation percent of TB dye in the aqueous solution was 98.7% within 10 min of light exposure. Several adsorption isotherms such as Langmuir, Freundlich, and Temkin adsorption isotherms have been tested in addition to the photocatalytic degradation kinetics. Both catalysts were found to follow the Langmuir isotherm model and pseudo-second-order kinetic model. Finally, the possible photocatalytic performance mechanism of Ag3PO4/G/SiO2 was proposed.

An insight into the diazo dye Direct Red 23 adsorption on Ca-modified biochar in an aqueous solution: An investigation based on DFT and molecular dynamics

Article

Jul 2024
SEP PURIF TECHNOL

Three dimensional nickel foam carried sea urchin-like copper-cobalt-cerium cathode for enhanced tetracycline wastewater purification in photocatalytic fuel cell

Article

Oct 2023
J COLLOID INTERF SCI

Treatment of polluted water with sunflower oil using advanced oxidation, modeling, kinetics and thermodynamics: A review

Conference Paper

Jan 2023

Treatment of landfill leachate using photocatalytic based advanced oxidation process - a critical review

Article

Aug 2023
J ENVIRON MANAGE

Landfill leachate is a discrete volumetric component of municipal solid waste; hence, researchers and professionals are more concerned about it because of its obscurity. Innovative treatment and emerging technologies are being scrutinized to address the treatment of landfill leachate challenges. The leading target of this review was to examine the possibility of removing recalcitrant organic pollutants from landfill leachate by photocatalytic-based advanced oxidation processes. A summary of the systematic applicability of conventional treatment for landfill leachate is provided, with a focus on physico-chemical and biological processes. The biological treatment, such as aerobic and anaerobic digestion, is an excellent technique for treating highly concentrated organic pollutants in the wastewater. However, Leachate can scarcely be treated using conventional techniques since it is enriched with refractory organics and inorganic ions. It is clear from the literature review that none of the available combinations of physico-chemical and biological treatments are entirely relevant for the removal of recalcitrant organic pollutants from leachate. Recently, the photo-assisted TiO2/ZnO oxidation has shown an excessively potential and feasible way to treat landfill leachate. TiO2/ZnO photocatalysis is currently developing to treat recalcitrant organic pollutants from landfill leachate. The effect of operating parameters reveals that pH and temperature affect the reaction rate. The addition of oxidant H2O2 to the TiO2/ZnO suspension suggests that TiO2 leads to an increase in the rate of reaction when compared to ZnO. Photocatalytic remediation technique of landfill leachate would support the goal of environmental sustainability by greatly enhancing the effectiveness of treated leachate reutilization. In this review, the selection of the best photocatalytic treatment for leachate based on its systematic relevance and potential conditions, characteristics, cost-effectiveness, essential controlling, discharge limit, long-term environmental effects, and its future study perspectives are emphasized and discussed.

Remediation of real industrial hypersaline effluent using sequential approach of precipitation followed by cavitation based oxidative process

Article

Jul 2023

Hydroxyapatite Supported Gold Nanoparticles Catalyzed Efficient Reduction of Nitroarenes and Degradation of Azo Dyes

Article

Full-text available

Jun 2023

Keya Layek

Gold nanoparticles supported on hydroxyapatite functions as a very efficient catalyst for the reduction of nitroarenes as well as for the degradation of azo dyes. The reaction takes place in aqueous medium at room temperature, using sodium borohydride as the source of hydrogen. The catalyst was prepared by a deposition–precipitation process using gold (III) chloride trihydrate solution containing hydroxyapatite as the support. The catalyst was thoroughly characterized by a pltehora of analytical techniques viz., TEM, HRTEM, FESEM, powder XRD, EDX and FTIR. The catalyst was then employed after optimization of reaction conditions. No additives or inert atmosphere was required and a very low loading of gold was sufficient enough to promote the reaction. Reaction kinetics studies were performed on the reduction of 4-nitrophenol to 4-aminophenol and a very high apparent rate constant of 1.63 × 10–2 s⁻¹ was obtained. Reaction kinetics studies have also been demonstrated for the degradation of methyl orange and congo red dyes. Appreciable apparent rate constants namely 8.678 × 10⁻³ and 3.464 × 10⁻³ s⁻¹ were obtained for the degradation of methyl orange and congo red dyes respectively. The catalyst was recoverable by simple centrifugation and can be reused for at least five reaction cycles.

Effect of Ag co-doped ZnO on the tartrazine photodegradation under solar irradiation

Article

May 2023

The existence of organic pollutants in water discharges has made wastewater treatment extremely difficult. This is mainly due to the release of various hazardous substances into waterways, which cause significant damage to humans and the aquatic ecosystem. This paper discusses the biosynthesis process of pure ZnO and Ag co-doped ZnO (1%Ag_ZnO and 2%Ag_ZnO). Highly pure nanoparticles (NPs) were obtained by simple and ecological route, through employment of Zn-nitrate as host and Ag-nitrate as dopant and phytochemicals of Zizyphus lotus fruit as reduction agent. The Ag_ZnO NPs were prepared in a one pot synthetic mode (1 and 2% Ag). The obtained samples were characterized by XRD analysis and FTIR spectroscopy which revealed the hexagonal Wurtzite structure of crystals with an average crystallite diameter varying from 16 to 29 nm. The elimination capability of NPs was investigated through the photo-degradation of tartrazine (TR) under solar light irradiation. The operating parameters namely the catalyst dose, initial TR concentration (Co) have been optimized for the TR degradation as function of time. The dye TR was more effectively removed by doped ZnO NPs under solar irradiation. The best performance was obtained with 2%Ag/ZnO, due mainly to the radicals O2·− and ·OH. Results indicated also that the TR removal rate increases with the increase in catalyst load and the decreased in the initial TR concentration.

Contribution of zeolite to remove malachite green in aqueous solution by adsorption processes: Kinetics, isotherms and thermodynamic studies

Article

Apr 2023

The textile industry produces huge amounts of wastewaters containing synthetic dyes. In the textile industry, acid, basic, reactive, dispersed chemicals are widely used for dyeing. The aim of this study was to evaluate the adsorption of malachite green onto zeolite from aqueous solutions was realized in batch system. The adsorbent was characterized by the Fourier transform infrared spectroscopy, X-ray analysis, and zero point charge (pHzpc = 10.42). However, some examined factors were found to have significant impacts on the adsorption capacity of zeolite such as the initial malachite green concentration (C o ), solution pH, adsorbent dose, agitation speed, particles size, and temperature. The best capacity was found at pH 8 with an adsorbent dose 0.2 g/l, an agitation speed 200 rpm and a contact time of 40 min. The kinetic adsorptions were found to follow rather a pseudo-second order kinetic model with a determination coefficient (R ² ) of 0.999. The equilibrium adsorption data for the malachite green adsorption onto the zeolite were analyzed by the Langmuir, Freundlich, Elovich, and Temkin models. The results indicate that the Langmuir model provides the best correlation with a capacity q max of 83.33 mg/g at 25°C. The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters, namely the free energy (ΔG°); enthalpy (ΔH°) and entropy (ΔS°) to predict the nature of adsorption. The positive values of ΔG° and ΔH° indicate that the overall adsorption is not spontaneous and endothermic with a physisorption process. The adsorbent elaborated from the zeolite was found to be efficient and suitable for the elimination of reactive dyes from aqueous solutions, due to its availability of adsorption sites, low cost preparation, and good uptake capacity.

Elaboration et caractérisation de photocatalyseurs à base de TiO2 et ZnO supportés sur PMMA : Application à la dégradation de colorants industriels

Thesis

Jul 2022

Omar Ounas

La photocatalyse hétérogène est une méthode très efficace comparée aux traditionnelles techniques pour le traitement des eaux contaminées. Elle présente plusieurs avantages dont on peut citer : - la bonne capacité à dégrader efficacement un spectre large de contaminants organiques jusqu’à leur minéralisation totale ainsi que leurs produits de transformation. – L’habilité à désinfecter ces eaux de microorganismes pathogènes. – Les conditions opératoires douces (T=25°C, P=1atm). 𝑇𝑖𝑂2 et ZnO restent les photocatalyseurs les plus utilisés et les plus documentés, grâce principalement à leur grande stabilité chimique, photostabilité, coût relativement faible, ainsi que leur faible toxicité. Le mécanisme d'utilisation de ces semi-conducteurs directement en suspension, présente l’inconvénient du passage par une étape de filtrage à la fin du traitement et donc le défi technique de séparer le catalyseur de la solution, une étape supplémentaire qui peut s’avérer couteuse. Pour y remédier, les recherches récentes penchent vers l’immobilisation des photocatalyseurs sur divers supports comme : verre, quartz, silice, charbon actif, textile, céramique ou même polymère. Cette immobilisation peut affecter la performance photocatalytique, la surface et l'adsorption du semi-conducteur, mais elle présente l'avantage de gérer l'eau contaminée en flux continu puisqu'elle élimine le besoin de séparer les particules de catalyseur une fois l'eau traitée. Dans ce contexte, nous avons procédé à la préparation de films par immobilisation de ZnO et 𝑇𝑖𝑂2 sur le support polymère poly méthacrylate de méthyle (PMMA). Ainsi, nous avons préparé des films photoctalytiques, nous les avons caractérisés par plusieurs techniques ; pHZPC, FTIR, DRX et Fluorescence X, et nous avons étudié leur effet sur la dégradation de polluants organiques (colorant : bleu de methylène et direct bleu 199) sous rayonnement UV (365nm). Investigation qui a été suivie par spectroscopie UV-visible et a donné une efficacité ne dépassant pas 70% avec apparition de phénomène d’adsorption/désorption. Les résultats trouvés ont pu être améliorés en entamant une étude de plans d’expériences visant à trouver les conditions optimales de traitement et d’étudier les effets des paramètres (pH, concentration du colorant, et concentration de l’agent d’amorçage 𝐻2𝑂2) mis en jeu. Étude qui a pu montrer que la concentration du colorant influe largement et que plus elle est élevée, plus les catalyseurs deviennent moins performants. Le pH présente aussi une grande importance ; il est toujours lié à la valeur du pHzpc du catalyseur et à la charge liée au type de polluant. Et, que 𝐻2𝑂2 ne présente d’effet que pour certaine valeur de pH ce qui montre l’interaction qui existe entre ces deux paramètres. Une optimisation des conditions opératoires a permis d’améliorer l’efficacité des catalyseurs avec une dégradation atteignant 85%.

A novel auto-combusted synthesis of MFC-800 nanoparticles: an efficient photocatalyst for degradation of industrial pollutant in environmental benign route

Article

Feb 2023

We have prepared MFC-800 nanoparticles (MnFe2O4 nanoparticles, calcinated at 800 °C) by a novel auto combustion technique for the degradation of TY (titan yellow) dye under the natural source of light and reduction process (aromatic nitro compounds, Ar-NO2 to Ar-NH2) in green circumstances. Different characterization techniques like FT-IR, UV–Vis, XRD, and SEM–EDX have been engaged for the confirmation of the production of MFC-800 nanoparticles. Various parameters were examined for obtaining better results in terms of degradation efficiency (%), like the amount (mg) of MFC-800 nanoparticles, dye concentration (ppm), amount (ml) of TY dye, and pH of TY dye solution. The prepared MFC-800 nanoparticles showed excellent catalytic activity of 94% for TY dye degradation. The MFC-800 nanoparticles in combination with NaBH4 smoothly reduces the 4-NP (4-nitrophenol) to 4-AP (4-aminophenol) in 75 s. Synthesized MFC-800 nanoparticles were easy to recover with the help of an external magnet from the reaction mixture. The developed system is simple and cost-effective, and no additional chemicals were used for the degradation process.

Potential of Titanium Dioxide to Remove Bromothymol Blue (BTB) in Aqueous Solution by Batch Mode Adsorption–Kinetic, Isotherm and Thermodynamic Studies

Article

Feb 2023

Moussa Abbas

The adsorption is widely used to remove certain classes of pollutants from water, especially those that are hardly biodegradable and dyes represent one of these problematic groups. The removal of bromothymol blue (BTB) from wastewater using TiO2 was studied in batch system. The adsorbent TiO2 has a specific surface area of 400 m2/g, a mean crystallites sizes (5–10 nm), and pHpzc equal to 6.5. TiO2 is stable over the whole pH range and constitutes a good compromise between efficiency and stability (in both acidic and basic media), therefore, the use of other additives is not necessary. Its non-toxicity and low energy required for its activation (E ~ 3 eV) as well as its low cost for most of the applications envisaged make it advantageous. The influence of effective variables such as solution pH (1–10), contact time (0–60 min), initial BTB concentration (5–40 mg/l), adsorbent dose of TiO2 (0.2–2 g/l), and temperature (20–60 °C) on the adsorption efficiency was examined, while the BTB content was determined by UV–Vis spectrophotometry. The optimal pH, adsorbent dose, and contact time for the efficient removal were found to be 10, 0.2 g/l, and 30 min, respectively, and the adsorbent was characterized by the BET analysis and point of zero charge (pHpzc). Among the different kinetic models, the experimental data of the BTB removal are well fitted with the pseudo-first-order kinetic model with a high determination coefficient. The evaluation of the fitness of equilibrium data by various conventional isotherm models, based on the R2 value as criterion, show the successful applicability of the Langmuir model for the interpretation of experimental data with a maximum adsorption capacity (qmax) of 27.02 mg/g at 20 °C and R2 of 0.997. The adsorption isotherms at different temperatures have been used for the determination of the free energy (ΔGo = 2.1808 to—1.0981 kJ/mol), enthalpy (ΔHo = 20.74 kJ/mol), and entropy (ΔSo = 65.58 J/mol/K) indicate that the overall adsorption is spontaneous and endothermic in nature.

The Effect of Mineral Ions Present in Tap Water on Photodegradation of Organic Pollutants: Future Perspectives

Article

Full-text available

Jan 2023

Photodegradation is the chemical conversion of large, toxic, and complex molecules into non-toxic, simpler, and lower molecular weight species due to light exposure. Heterogeneous photocatalysis has sufficient potential to degrade toxic organic pollutants present in wastewater. As industries discharge their effluents containing organic pollutants into natural water bodies, which penetrate into the subsurface through connected pores it is necessary to study this process in natural or tap water. Tap water (TW) is mainly obtained from underground wells having inorganic salts in a minute quantity with a conductivity of 500 μS/cm. TW contains inorganic anions, which affect the photocatalytic activity and photocatalysis process. The aim of this review is to evaluate the effect of TW on the photo-degradation of organic pollutants such as dyes, pharmaceutical products, pesticides , etc., with the support of the literature. The TW had a diverse effect on the photodegradation of organic pollutants; either it may enhance or decrease the rate of pollutants' photodegradation.

Structural and Optical Properties of Ni-Cu Doped TiO2 Synthesized by Sol-Gel Method

Article

Nov 2022

Ni-Cu doped TiO2 nanoparticles as photocatalyst were synthesized by simple sol-gel method. The effect of Ni and Cu doping on TiO2 and their structural and optical properties were analyzed by XRD, FT-IR, SEM-EDS, TEM and UV-DRS techniques. The XRD patterns of calcined nanoparticles showed a monophasic anatase structure with average diameter around 8 nm, which is in close agreement with the TEM results. The surface morphology of the prepared Ni-Cu doped TiO2 nanoparticles were also analyzed by SEM-EDS technique. From UV-DRS analysis, the band-gap energy value of Ni-Cu doped TiO2 nanoparticles was found to be 2.72 eV. The photocatalytic effect of Ni-Cu doped TiO2 nanoparticles as photocatalyst was studied under visible light irradiation through the degradation of Congo red azo dye. The photocatalytic results revealed that Ni-Cu doped TiO2 showed 99.6% degradation efficiency towards Congo red dye, whereas TOC analysis showed a complete mineralization of Congo red dye with minimum degradated byproducts. These results clearly elucidated that the synthesized photocatalyst is practically effective and is recovered easily, thus minimizing the operating costs. Due to the stability of Ni-Cu doped TiO2 nanoparticles, the prepared photocatalyst exhibit high degrading efficiency even after recycled several times.

Efficient photo‐degradation of cationic dyes by Co3O4 and Sr‐Co3O4 spinel nanocomposites under solar light irradiation

Article

Sep 2022

In the present study Co3O4 and Sr‐Co3O4 nanoparticles were prepared by sol‐gel and co‐precipitation methods and tested as photo‐catalysts for the degradation of methylene blue (MB, model molecule of the thiazine dyes class) and malachite green (MG, model molecule of the triphenylmethane category)under solar light irradiation. To study the photocatalytic activity, Co3O4 was doped by three different weight percentages of strontium (5%, 10%, and 15%). Among these, 10 wt% Sr‐Co3O4, named as (10)Sr‐Co3O4, showed maximum photodegradation efficiency toward both MB and MG. Their structural and morphological characteristics, chemical composition, surface area, and optical properties were investigated by FT‐IR spectroscopy, X‐ray diffraction (XRD), Field Emission Scanning Electron Microscopy – Energy Dispersive Spectroscopy (FE‐SEM‐EDX), UV–Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) analysis. The XRD investigations of Co3O4 and (10)Sr‐Co3O4 catalysts indicated retention of structure. The effect of initial pH, initial concentration of the dyes and photocatalysts dose was properly investigated. The results demonstrated the enhanced photocatalytic activity of (10)Sr‐Co3O4 compared to that of pristine Co3O4 due to Sr doping that improves electron‐hole (e–/h+) pairs separation mediated by charge migration on the Sr‐Co3O4 structure. The as‐prepared photocatalyst exhibited a remarkable photocatalytic efficiency towards both the dyes. (10)Sr‐Co3O4 and Co3O4 degraded 96% and 88% of MB at pH = 11, and 92% and 85% of MG at pH = 9, respectively in 90 min. Moreover, it was demonstrated that the photodegradation of MB and MG by Sr‐Co3O4 and Co3O4 followed a pseudo‐first‐order kinetics. Both the photocatalysts showed good stability during recycling maintaining high performances after five cycles. Finally, the active species were identified using various scavengers by trapping holes and radicals generated during the photocatalytic degradation process.

The efficiency of magnetic TiO2 anatase loaded by graphen quantum dots for photocatalytic degradation of imipramine from aquatic media

Article

Full-text available

Mar 2022

Synthesis and Characterization of Copper (II) Schiff Base Metal Complex for Environmental Remediation

Chapter

Jan 2022

The present work is focused on the synthesis and characterization of Schiff base ligand along with its metal complex from dialdehyde and primary amine. Repeated melting temperature and spectrum studies such as IR and 1HNMR were used to analyse the synthesised Schiff base and its corresponding metal complex. The photocatalytic degradation of Methylene blue (MB) dye was studied in the presence of an oxidising agent such as H2O2, spectrophotometrically by the synthesized Cu(II) metal complex on irradiation of visible light radiation. The degradation of MB dye was studied in terms of regular time interval. The outcomes clearly reveals that the MB dye can be degraded and almost mineralized completely by using the synthesised copper metal complex as a catalyst. The photocatalysis of complex were studied using various parameters including the impact of light irradiation period, concentration of catalyst, substrate concentration (MB dye), amount of H2O2 as oxidising agent, and effect of pH. The percentage degradation of MB was found more than ninety percentages in the visible light irradiation.KeywordsSchiff base ligandCopper metal complexPhotocatalytic degradationMethylene blue dye

Photocatalytic Degradation of Yellow-50 Using Zno/Polyorthoethylaniline Nanocomposites

Article

Full-text available

Mar 2022

Water pollution is the biggest concern among the scientific community due to the rapid increase in the industrial sector. The photocatalytic degradation of dyes using nanocomposites (NCs) has gained much attention for wastewater treatment. The NCs of polyorthoethylaniline (POEANI) with zinc oxide (ZnO) were fabricated through the chemical oxidative polymerization technique using orthoethylaniline monomer and nanoparticles of ZnO. The synthesized NCs were characterized by SEM, FT-IR, and XRD. The photocatalytic capability of ZnO/POEANI NCs was studied for the degradation of direct yellow 50 (DY50) in aqueous medium under sunlight. SEM analysis showed that the morphology of NCs as irregular clusters and zinc oxide was uniformly dispersed in the POEANI matrix. The maximum degradation of the dye DY50 was observed to be 68.8% after 110 min. The synthesized morphology of the materials can be confidently employed for the degradation of similar dyes in aqueous media.

Titanium Dioxide (TiO 2 ) based photocatalysis for textile wastewater treatment -its applications and biosafety -A Review

Article

Full-text available

Feb 2022

Photocatalysis is an efficient method that can be used in wastewater treatment to degrade the toxic dyes released from many textile and other industries. Titanium dioxide has proved to be an efficient photocatalyst that can be used for wastewater treatment. Moreover, it may be very well utilized as an antibacterial agent based on substantial oxidation movement and super hydrophilicity. TiO2 demonstrates relatively high reactivity and synthetic strength under UV light (λ<387nm), surpassing the bandgap of 3.3eV in the anatase crystalline stage. The improvement of photocatalysts showing high reactivity under visible light (λ> 400 nm) ensures the use of the principal part of the sunlight and therefore be utilized for efficient wastewater treatment. Broad utilization of TiO2 in various applications has raised many concerns regarding treated dyes and titanium nanoparticles' toxicity. Also, the dye wastewater rich in harmful azo compounds may generate highly toxic intermediates affecting aquatic life forms when treated using photocatalytic methods. Additionally, the nanoparticles may leach into the aquatic environment and may result in toxic effects on both the aquatic environment as well as on humans. This review talks about the potential use of TiO2 in the photocatalytic treatment of dye wastewater and the toxicities associated with them.

Photocatalytic Degradation Pathway of Methylene Blue in Water

Article

Full-text available

May 2001
APPL CATAL B-ENVIRON

The TiO2/UV photocatalytic degradation of methylene blue (MB) has been investigated in aqueous heterogeneous suspensions. In addition to a prompt removal of the color, TiO2/UV-based photocatalysis was simultaneously able to oxidize the dye, with an almost complete mineralization of carbon and of nitrogen and sulfur heteroatoms into CO2, NH4+, NO3− and SO42−, respectively. A detailed degradation pathway has been determined by a careful identification of intermediate products, in particular aromatics, whose successive hydroxylations lead to the aromatic ring opening. These results suggest that TiO2/UV photocatalysis may be envisaged as a method for treatment of diluted waste waters in textile industries.

Aggregation of o,o′- Dihydroxy azo Dyes III. Effect of cationic, anionic and non-ionic surfactants on the electronic spectra of 2-hydroxy-5-nitrophenylazo-4-[3-methyl-1-(4″-sulfophenyl)-5-pyrazolone]

Article

Feb 2000
DYES PIGMENTS

The effect of Septonex, TX-100 and SDS surface-active agents on the aggregation, the acid-base, and the optical properties of 2-hydroxy-5-nitrophenylazo-4-[3-methyl-1-(4″-sulfophenyl)-5-pyrazolone] was studied by the spectrophotometric method. The study was performed in submicelle and micelle surfactant concentration, and at different dye/surfactant concentrations in a buffered system. Both the aqueous and micellar dissociation constants of the dye under investigation were evaluated at 22±1°C. The changes in the absorption pattern resulted from the addition of surfactants at different pHs, where different species exist, and is explained on the basis of electrostatic interactions between the different existing dye species (azo/hydrazo/dimer/monomer) and the surfactant micelles and pre-micellar aggregates. Different tautomeric forms of the dye are suggested based on the different spectral changes. A model for the interaction between surfactants and the different dye species is proposed. This model explains both the observed spectral changes in micellar solution and the obtained micellar dissociation constants of the dye.

Recent advances in high quantum yield dye sensitization of semiconductor electrodes

Article

Apr 1992
ELECTROCHIM ACTA

Recent advances in the study of the dye sensitization of semiconductor electrodes are reviewed highlighting the characteristics of dye/semiconductor pairs with a high quantum yield, Φ, for electrons collected as current per photon absorbed by the dye. Photoelectrochemical data, picosecond fluorescence measurements, and flash photolysis results on high Φ systems are discussed in relation to kinetic models of the injection process in order to provide an overall evaluation of the current state of the understanding of the event following excitation of an excited dye adsorbed on a semiconductor surface.

Heterogeneous Photocatalytic Oxidation of Cyanide and Sulfite in Aqueous Solutions at Semiconductor Powders

Article

Jul 1977

The photocatalytic oxidations of CN- and SO32- were studied at several semiconductor powders including TiO2, ZnO, CdS, Fe2O3, and WO3 using a xenon light source. TiO2, ZnO, and CdS were active photocatalysts for cyanide oxidation, while no oxidation was seen for Fe2O3 and WO3. The catalyzed oxidation of CN- at TiO2 using sunlight was also investigated. The rate constant for CN- oxidation at TiO2 in sunlight was 3.1 × 10-6 mol day-1 cm-2 illuminated surface. The product of the oxidation of CN- at TiO2 was quantitatively determined to be OCN-. TiO2, ZnO, CdS, and Fe2O3 photocatalyzed the oxidation of SO32-. The order of the catalytic activity was Fe2O3 ∼ ZnO ∼ CdS > TiO2. The rates of the photocatalytic oxidations were greater for SO32- than for CN- in the cases of TiO2, ZnO, and CdS. The chemical and photochemical stabilities for the most active catalysis were determined.

Photocatalytic degradation of various dyes by combustion synthesized nano anatase TiO2

Article

Sep 2003
APPL CATAL B-ENVIRON

The 8–10 nm pure anatase phase titania with 156 m2/g BET surface area was prepared by solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and BET surface area. This catalyst was used for the photocatalytic degradation of various dyes such as heteropolyaromatic dye (Methylene blue), anthraquinonic dye (Alizarin S), and azoic dyes (Methyl red, Congo red, and Orange G). The effect of catalyst loading, initial concentrations of the dyes, pH, and transition metal doping on TiO2 was investigated. Substitution of TiO2 with transition metal had a detrimental effect on the photocatalytic activity. However, this inhibition effect was not observed with Pt impregnated TiO2. This was attributed to the metals being in ionic state in metal substituted TiO2 synthesized by combustion method, and zero state of metal in impregnated catalysts as evidenced by XPS study. The degradation of dyes was also investigated in solar exposure. The photoactivity of the combustion synthesized titania was higher than commercial TiO2 (Degussa P-25) for both UV and solar exposure. The experimental data followed Langmuir–Hinshelwood (L–H) rate form and the kinetic parameters were obtained.

Effect of Acidity and Inorganic Ions on the Photocatalytic Degradation of Different Azo Dyes

Article

Oct 2003
APPL CATAL B-ENVIRON

Effects of acidity and inorganic ions that are common in industrial effluent on the photocatalytic degradation of azo dyes, Procion Red MX-5B (MX-5B) and Cationic Blue X-GRL (CBX), have been investigated in UV illuminated TiO2 dispersions. There are significant differences between adsorption and photodegradation of MX-5B and those of CBX to the change of solution pH. The results indicated that CBX photodegradation was favored at the surface of TiO2, while that of MX-5B occurred in the aqueous phase. At pH 2.4, SO42−, H2PO4−, ClO4− and F− in general increased the decolorization rates of MX-5B and CBX by enhancing the adsorption of the selected dyes on the surface of TiO2. At pH 10.8, most of the selected anions inhibited the photocatalytic oxidation (PCO) to decolorize and degrade CBX and MX-5B. These results demonstrated that inorganic anions affect the photodegradation of dyes by their adsorption onto the surface of TiO2 and trapping positive hole (h+) and OH. Inorganic cationic ions, such as Cu2+ and Ni2+ had strong inhibition on the PCO decolorization of MX-5B at pH 10.8. On the contrary, no significant effect was observed at the same concentration of metal cations at pH 2.4.

Photochemical and Photocatalytic Degradation of an Azo Dye in Aqueous Solution by UV Irradiation

Article

Feb 2003
J PHOTOCH PHOTOBIO A

The photochemical and photocatalytic degradation of aqueous solutions of Solophenyl Green (SG) BLE 155%, an azo dye preparation very persistent in heavy colored textile waters, has been investigated by means of ultraviolet (UV) irradiation. The pure photochemical process demonstrated to be very efficient for low initial concentrations of the dyestuff. For higher concentrations the photocatalyitic degradation was carried on using commercial titanium dioxide, and mixtures of this semiconductor with different activated carbons (AC) suspended in the solution. The kinetics of photocatalytic dyestuff degradation were found to follow a first-order rate law. It was observed that the presence of the activated carbon enhanced the photoefficiency of the titanium dioxide catalyst. Differently activated carbon materials induced different increases in the apparent first-order rate constant of the process. The effect was quantified in terms of a synergy factor (R) already described in the literature. The kinetic behavior could be described in terms of a modified Langmuir–Hinshelwood model. The values of the adsorption equilibrium constants for the organic molecules, KC, and for the reaction rate constants, kC, were 0.0923 l mg−1 and 1.58 mg l−1 min−1 for the TiO2/UV process and 0.0928 l mg−1 and 2.64 mg l−1 min−1 for the TiO2+AC/UV system with highest synergy factor, respectively. The mechanism of degradation was discussed in terms of the titanium dioxide photosensitization by the activated carbon.

The effect of operational parameters and TiO2-doping on the photocatalytic degradation of azo-dyes

Article

Nov 1999
CATAL TODAY

The photocatalytic degradation of Acid Orange 7 (AO7), a non-biodegradable azo-dye, has been investigated over TiO2 photocatalysts irradiated with a light source simulating solar light. The effect of operational parameters, i.e., dye concentration, photocatalyst content, pH of the solution and incident light energy on the degradation rate of aqueous solutions of AO7 has been examined. The effect of incorporating cations with valence higher (W6+) and lower (Ca2+) than the parent cation (Ti4+) in the TiO2 matrix has also been investigated. Results show that the employment of efficient photocatalysts and the selection of optimal operational parameters may lead to complete decolorization and to substantial decrease of the Chemical Oxygen Demand (COD) of the dye solutions.

TiO2-Assisted Photocatalytic Degradation of Azo Dyes in Aqueous Solution: Kinetic and Mechanistic Investigations: A Review

Article

Apr 2004
APPL CATAL B-ENVIRON

The photocatalytic degradation of azo dyes containing different functionalities has been reviewed using TiO2 as photocatalyst in aqueous solution under solar and UV irradiation. The mechanism of the photodegradation depends on the radiation used. Charge injection mechanism takes place under visible radiation whereas charge separation occurred under UV light radiation. The process is monitored by following either the decolorization rate and the formation of its end-products. Kinetic analyses indicate that the photodegradation rates of azo dyes can usually be approximated as pseudo-first-order kinetics for both degradation mechanisms, according to the Langmuir–Hinshelwood model. The degradation of dyes depend on several parameters such as pH, catalyst concentration, substrate concentration and the presence of electron acceptors such as hydrogen peroxide and ammonium persulphate besides molecular oxygen. The presence of other substances such as inorganic ions, humic acids and solvents commonly found in textile effluents is also discussed. The photocatalyzed degradation of pesticides does not occur instantaneously to form carbon dioxide, but through the formation of long-lived intermediate species. Thus, the study focuses also on the determination of the nature of the principal organic intermediates and the evolution of the mineralization as well as on the degradation pathways followed during the process. Major identified intermediates are hydroxylated derivatives, aromatic amines, naphthoquinone, phenolic compounds and several organic acids. By-products evaluation and toxicity measurements are the key-actions in order to assess the overall process.

Visible Light and Fe(III)-Mediated Degradation of Acid Orange 7 in the Absence of H2O2

Article

Jul 2003
J PHOTOCH PHOTOBIO A

The photodegradation of Acid Orange 7 (AO7) was successfully achieved in the presence of Fe(III) ions only under visible light (λ≥420 nm). Upon adding Fe(III) to AO7 solution, ferric ions formed complexes with AO7 mainly through the azo chromophoric group. This AO7–Fe(III) complex formation was highly pH-sensitive and maximized around pH 3.7. The visible light-induced degradation of AO7 was effective only when the complex formation was favored. The AO7 photodegradation accompanied the production of ferrous (Fe2+) ions and was not inhibited in the presence of excess OH radical scavenger (2-propanol), which indicated that OH radicals were not responsible for the dye degradation. The proposed mechanism of the dye degradation is the visible light-induced electron transfer from the azo chromophoric group to the iron center in the complex. Therefore, when the formation of AO7–Fe(III) complex was inhibited in the presence of excess interfering anions such as sulfites and sulfates, the photodegradation of the dye was also prevented. The photodegradation of AO7 under visible light produced o-phthalate and 4-hydroxybenzenesulfonate (4-HBS) as major products but did not reduce the total organic carbon (TOC) concentration. Since this process does not require the addition of hydrogen peroxide, it might be developed into an economically viable method to pretreat or decolorize azo-dye wastewaters using sunlight.

Photocatalytic Degradation of Azo Dye Acid Red 14 in Water: Investigation of the Effect of Operational Parameters

Article

Apr 2003
J PHOTOCH PHOTOBIO A

Acid Red 14 (AR14), commonly used as a textile dye, could be photocatalytically degraded using TiO2 suspensions irradiated by a UV-C lamp (30 W). The experiments showed that TiO2 and UV light had a negligible effect when they were used on their own. The semi-log plot of dye concentration versus time was linear, suggesting first order reaction (K=1.41×10−2 min−1). The effects of some parameters such as pH, the amount of TiO2 and initial dye concentration were also examined.The photodegradation of AR14 was enhanced by the addition of proper amount of hydrogen peroxide, but it was inhibited by ethanol. From the inhibitive effect of ethanol it was deducted that hydroxyl radicals played a significant role in the photodegradation of dye, but a direct oxidation by positive holes was probably not negligible. Accordingly, it could be stated that the complete removal of color, after selecting optimal operational parameters could be achieved in a relatively short time, about 3.5 h.

Solar/UV-induced photocatalytic degradation of three commercial textile dyes

Article

Feb 2002
J HAZARD MATER

The photocatalytic degradation of three commercial textile dyes with different structure has been investigated using TiO(2) (Degussa P25) photocatalyst in aqueous solution under solar irradiation. Experiments were conducted to optimise various parameters viz. amount of catalyst, concentration of dye, pH and solar light intensity. Degradation of all the dyes were examined by using chemical oxygen demand (COD) method. The degradation efficiency of the three dyes is as follows: Reactive Yellow 17(RY17) > Reactive Red 2(RR2) > Reactive Blue 4 (RB4), respectively. The experimental results indicate that TiO(2) (Degussa P25) is the best catalyst in comparison with other commercial photocatalysts such as, TiO(2) (Merck), ZnO, ZrO(2), WO(3) and CdS. Though the UV irradiation can efficiently degrade the dyes, naturally abundant solar irradiation is also very effective in the mineralisation of dyes. The comparison between thin-film coating and aqueous slurry method reveals that slurry method is more efficient than coating but the problems of leaching and the requirement of separation can be avoided by using coating technique. These observations indicate that all the three dyes could be degraded completely at different time intervals. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams.

The influence of FeCl3 on the photocatalytic degradation of dissolved azo dyes in aqueous TiO2 suspensions

Article

Nov 2003
CHEMOSPHERE

The study concerned decolouration of solutions of azo, anionic (Acid Orange 7, Reactive Red 45, Acid Yellow 23) and cationic (Basic Blue 41 and Basic Orange 66) dyes during illumination with UV (lambdamax 366 nm) irradiation in the presence of TiO2 and FeCl3. The process of decolouration during illumination of the solutions studied containing FeCl3 underwent significant intensification in the case of anionic dyes and unfavourable inhibition in case of cationic dyes. It was also observed that FeCl3 had a diverse influence on the adsorption of the dyes studied on TiO2. The adsorption of anionic dyes and decolouration of solutions before the illumination was observed only in the presence of FeCl3. In case of cationic dyes the addition of FeCl3 caused elimination of these phenomena. An additional cause of decolouration of anionic dyes solutions before illumination was the precipitation of their poorly soluble compounds from Fe3+. The processes of degradation and mineralization of the dye that accompanied decolouration of Acid Orange 7 solutions were also observed. It was stated that similarly to the case of Acid Orange 7, the decolouration of the studied anionic dyes' solutions can depend on the concentration of FeCl3, the amount of TiO2 and the initial concentration of the dye in its solution.

Analyses of carcinogenic aromatic amines released from harmful azo colorants by Streptomyces SP. SS07

Article

Dec 2003
J CHROMATOGR A

Extracellular fluid protein (ECFP) of Streptomyces species SS07 has been used to reduce water soluble azo dyes and the carcinogenic amines released have been compared with that from chemical reduction. The effect of temperature, pH and contact time on the recovery of amines using ECFP was studied. The ECFP releases carcinogenic amines at a pH of 9.2 and a temperature of 37 degrees C for a contact period of 24 h. The reduction products were analyzed with HPLC and their structures confirmed by LC-MS and GC-MS. It was observed that both the ECFP and chemical reduction methods released similar type of amine products. In the case of dye samples, compared to chemical reduction, 5-20% increase in the release of carcinogenic amines by ECFP was observed. The percentage of amine products released by chemical reduction was higher for leather garment samples compared to ECFP treatment.

The Effect of Operational Parameters on the Photocatalytic Degradation of Three Azo Dyes in Aqueous TiO2 Suspensions

Abstract

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