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Kinetics of Photocatalytic Degradation of Methylene Blue in a TiO2 Slurry Reactor

December 2010
Research Journal of Chemistry and Environment 14(4):9-13

Authors:

Sheetal Ovhal

Indiana University Bloomington

Pragati Thakur

Savitribai Phule Pune University

Textile industry effluents contain large number of dyes. Dyes are found to be toxic and considered to be resistant to biodegradation. Methylene blue (MB) is a representative of a class of dyestuffs resistant to biodegradation. In this work a detailed and systematic investigation of heterogeneous photocatalytic degradation of MB in aqueous TiO 2 suspension is presented using 8W low-pressure 'mercury vapor lamp with a focus to study the effect of various experimental parameters such as initial concentration of MB, concentration of TiO 2 as well as addition of electron scavenger H 2O 2 to obtain complete degradation and decolorization of MB. Degradation was found to increase in the order UV+TiO 2+H 2O 2 > UV+TiO 2 > UV+H 2O 2 > UV. The photodegradation of MB was monitored spectrophotometrically by estimating molar concentration changes of MB according to the Beer-Lambert's law. The rate constants for this heterogeneous photocatalysis were evaluated as a function of concentration of MB, H 2O 2 and TiO 2. A pseudo-first order kinetic has been used to describe the results.

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Research Journal of Chemistry and Environment______________________________________Vol.14 (4) Dec. (2010)

Res.J.Chem.Environ

(9)

Kinetics of Photocatalytic Degradation of Methylene Blue

in a TiO2 Slurry Reactor

Ovhal Sheetal D. and Thakur Pragati*

Department of Chemistry, University of Pune, Ganeshkhind, Pune, INDIA

*dr.pragati_thakur@rediffmail.com

Abstract

Textile industry effluents contain large

number of dyes. Dyes are found to be toxic and

considered to be resistant to biodegradation.

Methylene blue (MB) is a representative of a class of

dyestuffs resistant to biodegradation. In this work a

detailed and systematic investigation of heterogeneous

photocatalytic degradation of MB in aqueous TiO2

suspension is presented using 8W low-pressure

mercury vapor lamp with a focus to study the effect of

various experimental parameters such as initial

concentration of MB, concentration of TiO2 as well as

addition of electron scavenger H2O2 to obtain

complete degradation and decolorization of MB.

Degradation was found to increase in the order

UV+TiO2+H2O2 > UV+TiO2 > UV+H2O2 > UV. The

photodegradation of MB was monitored spectropho-

tometrically by estimating molar concentration

changes of MB according to the Beer-Lambert’s law.

The rate constants for this heterogeneous

photocatalysis were evaluated as a function of

concentration of MB, H2O2 and TiO2. A pseudo-first

order kinetic has been used to describe the results.

Keywords: Titanium dioxide, Hydrogen peroxide, Methyl-

ene blue, Photocatalyst.

Introduction

In recent years, heterogeneous photocatalysis on

metal oxide semiconductor particles has attracted

increasing attention as a promising method for the removal

of toxic organics from water1-3. It utilizes low intensity

ultraviolet light with semiconductors acting as

photocatalyst and leads to complete mineralization of

pollutants to environmentally harmless compounds. The

photocatalytic reactions allow thermodynamically

unfavorable reactions to occur and allow destruction of

non-biodegradable refractory contaminants. While catalytic

processes require high temperature or high pressure,

photocatalytic oxidation is a promising technique for many

purposes due to its ability to operate at or slightly above

ambient conditions4. A variety of organic molecules can be

photocatalytically oxidized and eventually mineralized

according to the following general reaction5-8:

Semiconductor, hν

Organic molecules + O2 CO2+H2O + mineral

acids

The photocatalysts commonly used are TiO2, ZnO,

CdS, Fe2O3, WO3 with TiO2 being frequently reported as

the most active in organic degradation experiments. In

wastewater treatment processes involving semiconductors,

non toxicity and insolubility, both in dark and on illum-

ination, are important considerations. TiO2 satisfies these

requirements; moreover, it is extremely stable in aqueous

suspensions with diminishing rate of photo corrosion.

Textile dyes represent the main source for aquatic

pollution with colored compounds. Several studies on

photocatalytic degradation of various photostable dyes have

been reported in the literature10. During dyeing process of

textile industry, approximate amounts of 1-15% are

discharged in wastewater 11. Dyes constitute more complex

entities and present a significant challenge to

environmental chemists because of the persistent

environmental health risks12. Cationic dyes are extensively

used for dyeing cotton, wool and silk. The risk of the

presence of these dyes in wastewater may arise from the

burns effect of dye, nausea, vomiting and diarrhea.

Reactive dye such as a Methylene Blue (MB) dye is widely

used in the textile industries because of the simple dyeing

procedure and stability during washing process13.

The data reported recently in the literature on the

photocatalyzed degradation of certain dyes by

heterogeneous photocatalytic processes are not sufficient

for industrial or for large scale pilot plant applications

because several experimental parameters e.g. light

intensity, reactor geometry, pH, temperature, concentration

of reactant and concentration of TiO2 have complex effects

on the degradation reaction and thus also on treatment

cost14. It was reported that the use of inorganic oxidants

such as H2O2, ClO3-, BrO3- and S2O8- in TiO2 system

increase the quantum efficiencies either by inhibiting

electron-hole pair recombination through scavenging

conduction band electrons at the surface of TiO2 or by

offering additional oxygen atom as an electron acceptor to

form the superoxide radical ion(O2-.).15-17 According to the

investigation on H2O2, adequate dose of H2O2 leads to a

faster degradation of organic compounds in the TiO2

photocatalytic system.18 However the degradation is

suppressed if excess H2O2 is used. This is due to the

undesirable consumption of OH. radicals that are

previously formed by H2O2 leading to generation of less

reactive HO2. radicals instead.19

Herein, we have investigated the systematic study

on the photocatalytic degradation of MB in aqueous TiO2

Research Journal of Chemistry and Environment______________________________________Vol.14 (4) Dec. (2010)

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suspension under UV light irradiation with a focus to study

the effect of various experimental parameters such as initial

concentration of MB, concentration of TiO2 as well as

addition of electron scavenger e.g. H2O2 to obtain complete

degradation and decolorization of MB.

Material and Methods

Reagents: TiO2 (LR grade Merck with 99 % purity:

mixture of anatase and rutile) of band gap = 3.2 eV and

BET surface area of 50 ± 15 m2g-1 , H2O2 (30%, w/w,

Merck), Methylene blue (Qualigens Fine Chemicals) were

used as received.

Photoreactor: The experiments were carried out in batch

immersion well photocatalytic reactor procured from

‘Scientific Aids and Instruments Corporation’, Chennai,

India. The reactor consists of double wall immersion well

made of quartz which was placed inside the glass reactor

fitted with standard joint. The whole assembly of the

reactor as procured from the manufacturer also consists of

8W low-pressure mercury vapor lamp (peak emission at

254 nm) which was placed inside the immersion well.

Water was circulated through the inlet and outlet provided

by the reactor in order to maintain the constant temperature

between 30 ± 10C.

Analysis: Effect of various experimental parameters such

as time of irradiation, catalyst concentration, substrate

concentration and effect of addition of electron scavenger

H2O2 was studied. For that, from the stock solution of MB

of concentration 0.01 mol/L, various solutions of desired

concentrations were prepared in Millipore water. The

photodegradation experiments were carried out in

photoreactor in which 250 ml of MB solution was taken.

The solution was agitated with the help of aeration pump

and magnetic stirrer. To study the effect of time of irradia-

tion, photocatalytic degradation of MB was studied over

the range of 3-8 hrs. Fig.2 shows spectral changes

occurring during the photo degradation of MB. Effect of

catalyst and H2O2 concentration was studied by varying the

amounts of TiO2 ranging from 50 to 125mg/250mL and

0.2g to 0.6g/250mL for H2O2. For the optimized catalyst

concentration, various experiments were carried for the

substrate concentration of MB ranging from 1.0x10-5

to1.0x10-4mol/L. When TiO2 was used, the suspension was

stirred in the dark for 30 min before irradiation which was

found to be sufficient to reach an equilibrated adsorption.

The suspension was then irradiated with UV lamp. In each

case the suspension was sampled at convenient time,

filtered through 0.2 μm, 13 mm diameter millipore disc and

then analyzed by Schimadzu UV-Visible Spectro-

photometer (UV-1650PC) to measure the concentration of

dye in suspension.

Results and Discussion

Kinetics of MB disappearance: Fig.3 shows the kinetics

of the disappearance of MB on initial concentration of

5.0x10-5 mol/L under different conditions. There was no

observable loss of MB when the irradiation was carried out

in the absence of TiO2. The presence of TiO2 and H2O2

combination shows rapid degradation of MB. Experimental

results are presented in fig.3 and table 1, together with

correlation coefficients for each of the fitted lines. The

results show that the degradation rate depends on different

experimental conditions.

This fitting indicates that the photocatalytic

degradation of MB in aqueous TiO2 suspensions can be

described by the pseudo- first order kinetic model. As it can

be seen from the values given in table1, the change in the

rate constant is 0.0351h-1when the reaction condition is

only UV and 0.9096 h-1 when the reaction condition is UV

and TiO2 along with H2O2 .This shows that rate of reaction

is UV+ TiO2+ H2O2> UV+ TiO2 > UV+ H2O2 >UV. The

UV+ TiO2+ H2O2 system shows higher rate of degradation

as compared to the UV+ TiO2 because the addition of

hydrogen peroxide to the system increases the

concentration of OH., since it inhibits the electron-hole

recombination, according to the following equation20:

TiO2 (e-) + H2O2= TiO2 + OH- + OH.

Effect of TiO2 concentration on MB degradation: The

effect of varying concentration of TiO2 was studied.

Experiments were performed with various amounts of

catalyst powder (50 – 125 mg / 250 ml) at 5.0x10 -5 mol/L

initial concentration of MB. The curve in fig.3 shows that

% degradation goes on increasing with an increase in the

TiO2 concentration up to 100 mg and then it is decreased.

As the concentration of catalyst is increased, the number of

photons absorbed and the number of MB dye molecules

adsorbed are increased owing to an increase in the number

of TiO2 particles. The density of particles in the area of

illumination also increases and so the rate is enhanced15.

Maximum degradation was obtained at a TiO2

concentration of 100 mg/250ml.

Beyond this the substrate molecules available are

not sufficient for adsorption by the increased number of

TiO2 particles. Hence the additional catalyst powder is not

involved in catalyst activities and the rate does not increase

with an increase in the amount of catalyst beyond a certain

limit21. Also at high TiO2 concentrations particles aggregate

which reduce the interfacial area between the reaction

solution and the photocatalyst. Thus the number of active

sites on the catalyst surface decreases. The increase in

opacity and light scattering by the particles may be the

other reasons for the decrease in the degradation rate.22

Effect of initial substrate concentration on MB degrad-

ation: The effect of substrate initial concentration on degr-

adation of MB dye was studied at different concentrations

varying from 5x10-5to 1x10-4mol/L since the pollutant

concentration is a very important parameter in water trea-

tment. Experimental results are presented in fig.4 and table

3 which show that the degradation rate depends on the

Research Journal of Chemistry and Environment______________________________________Vol.14 (4) Dec. (2010)

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initial concentration of MB. The rate constant k decreases

with increase in the initial concentration of MB which

confirms that kinetics of MB is not a simple first order but

pseudo first order. Furthermore, the slopes of the lines in

fig.5 and the k values in table 3 show that the degradation

rate decreases with increases in initial concentration.

The initial concentration dependence of the

photodegradation rate of MB can be based on the fact that

the degradation reaction occurs on TiO2 particles as well as

in solution. With an increase in dye concentration, the

solution becomes more intense colored and the path length

of photons entering the solution is decreased thereby fewer

photons reached the catalyst surface. Hence, the production

of hydroxyl and superoxide radicals is reduced.

Therefore, the photo degradation efficiency is

reduced23. Moreover, at the higher concentration, the

number of collisions between dye molecules increases

whereas the number of collisions between dye molecules

and .OH radical decreases. Consequently, the rate of

reaction is retarded.24-25 From fig.4, it can be seen that the

degradation rate constant obtained in this study is

proportional to the reciprocal of the initial MB

concentration.

Effect of addition of H2O2 on MB degradation: The

effect of addition of H2O2 to the system with optimized

catalyst concentration and optimized initial substrate

concentration was studied. For these studies, the amount of

H2O2 added ranged from 0.2g/250mL to 0.6g/250mL. The

obtained results are depicted in fig.6 and table 4 which

show pseudo-first order kinetics. Maximum degradation

rate was obtained for 0.4g of H2O2 concentration. The

addition of H2O2 to the heterogeneous system increases the

concentration of OH. radicals:

TiO2 (e-) + H2O2 → TiO2 + OH - + OH.

Being an electron acceptor, H2O2 does not only

generate .OH radicals but it also inhibits electron hole

recombination process at the same time, which is one of the

most important practical problems in using TiO2 as

photocatalyst. When the H2O2 concentration becomes high,

the excess H2O2 consumes hydroxyl radicals and it

performs like a hydroxyl radical scavenger26:

H2O2 + .OH → HO2. + H2O

Maximum rate of degradation was achieved in the

first hour only. Complete degradation was achieved in 3 hrs

after addition of H2O2.

Conclusion

The results obtained in the present study show the

great efficiencies of advanced oxidation processes in the

degradation of MB dye which are resistant to other

conventional treatment processes. Degradation was found

to increase in the order UV+TiO2+H2O2 > UV+TiO2 >

UV+H2O2 > UV. The photodegradation followed pseudo-

first order kinetics and was dependant on concentration of

TiO2, initial concentration of substrate and hydrogen

peroxide concentration.

The photo degradation rate goes through a

maximum when increasing the concentration of TiO2 due to

particle aggregation and reduction in the interfacial area

between the reaction solution and the photocatalyst. The

employment of UV+TiO2+H2O2 process led to complete

decolorization and degradation of MB.

In presence of high H2O2 concentration, the excess

H2O2 consumes hydroxyl radicals and performs like a

hydroxyl radical scavenger giving maximum photo degra-

dation rate at 0.4 g/L. The observations of this investigation

clearly demonstrated the importance of choosing the

optimum degradation parameters which are essential for

any practical application of photocatalytic oxidation proc-

ess. Obtained results of applications of heterogeneous

photocatalysis along with H2O2 with high degradation rate

make it the most appealing choice for MB degradation.

Acknowledgement

First author is thankful to University Grant

Commission (UGC), New Delhi and Center for Nano ma-

terials and Quantum Systems (CNQS), Department of

Physics, University of Pune, for financial support.

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Table I

Pseudo-first order kinetics data for the different

processes

Process k(h-1) R2

UV 0.0351 0.9817

UV/ H2O2 0.6423 0.9851

UV/TiO2 0.7066 0.9760

UV/TiO2/H2O2 0.9096 0.9819

Table II

Effect of concentration of TiO2 on photogradation rate

of MB

Weight of TiO2(g)

per 250 mL k(h-1) R2

50 0.2394 0.9579

75 0.3894 0.9691

100 0.7069 0.9749

125 0.3441 0.9765

Table III

Effect of initial concentration of MB on photogradation

rate

C0 mol/L k(h-1) R2

0.000010 1.5689 0.9955

0.000050 0.7684 0.9562

0.000067 0.3167 0.9615

0.000100 0.1044 0.9843

Table IV

Effect of H2O2 addition on the photodegradation rate of

H2O2 g

/250 mL k(h-1) R2

0.0 0.7024 0.9869

0.2 0.8518 0.9637

0.4 0.9240 0.9574

0.6 0.7840 0.9724

Fig. 1: Schematic representation of the processes occurring

in and on semiconductor particles during the photo

catalytic mineralization of organic molecules by oxygen.

OH. + Pollutants

CO2 + H2O

Research Journal of Chemistry and Environment______________________________________Vol.14 (4) Dec. (2010)

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Fig. 2 : Spectral changes occurred during

photodegradation of MB dye after time interval of 60

minute pH = 5.58, TiO2 = 100 mg/250 mL,

[MB] = 5 x 10-5 mol/L

Fig. 3: Effect of different experimental conditions on the

photodegradation of MB

pH = 5.58, TiO2 = 100 mg, [MB] = 5 x 10-5 mol/L

Fig. 4: Effect of TiO2 concentration on the photo

degradation rate of MB

pH = 5.58, [MB] = 5 x 10-5 mol/L

Fig. 5: Effect of initial concentration of MB on the

photo degradation rate

pH = 5.58, TiO2 = 100 mg/250 mL

Fig. 6: Effect of initial concentration of H2O2 on the

photo degradation rate, pH = 5.58,

TiO2 = 100 mg/250 mL, [MB] = 5 x 10-5 mol/L

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(Received 28th June 2010, accepted 15th November 2010)

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Abs.

Irradiation time in hrs

In C/C0

TiO2 in mg/250mL

Degradation

In C/C0

Irradiation time in hrs

In C/C0

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Aug 2020
J CHEM TECHNOL BIOT

Background Photocatalytic degradation of Orange II (OII) dye has been carried out with commercially available materials, namely sodium Y zeolite (NaY), ammonium Y zeolite (NH4Y), and reduced graphene oxide (RGO). The catalysts were characterized by N2 adsorption at −196 °C, pH at the point of zero charge (pHpzc), and ultraviolet/visible (UV/Vis) diffuse reflectance absorbance. The initial screening of processes like adsorption, oxidation with hydrogen peroxide alone, direct photolysis, combination of H2O2 with the catalyst, and/or with UV/Vis radiation has been done. For the process with better performance (radiation combined with the oxidant and using the materials as photocatalysts), a parametric study was carried out to evaluate the effect of pH, H2O2 concentration, catalyst dose, radiation intensity, and radiation type (UV/Vis or visible radiation) in OII degradation and mineralization. Results The screening demonstrated that radiation plays an important role in the hydroxyl radical formation and, inherently, in the oxidation of OII and in the mineralization of the organic compounds formed. Still, for all catalysts tested, the existence of optima in terms of pH (2.0), catalyst dose (100 mg L⁻¹), and H2O2 concentration (6 mM) was found, while the maximum radiation intensity (500 W m⁻²) and UV/Vis radiation incidence benefits the oxidation process. However, the best process performance was achieved when using the catalyst that absorbs more radiation (RGO), yielding OII and TOC removals of 97.7% and 87.9%, respectively, after 90 min of reaction time. Conclusion Taking into account the great performance reached, a possible application of such catalysts in the treatment of textile dyeing effluents is anticipated. © 2020 Society of Chemical Industry (SCI)

Hybrid photocatalytic/photochemical degradation of 1,2‑dichlorobenzene: kinetic, thermodynamic, operating cost, synergism and mineralization study

Article

Jun 2024
J IRAN CHEM SOC

This study investigates the combined effects of UV/TiO2 and UV/H2O2 processes on the degradation of 1,2-dichlorobenzene in aqueous media, employing a recycled current photo-reactor equipped with a water jacket. Evaluation of various factors—initial pH, TiO2 dosage, initial H2O2 concentration, pollutant concentration, and temperature—contributed to the optimization of degradation rates and operational costs for both processes. For the degradation of 50 mg/L of DCB, the optimal operating conditions were found to be for UV/TiO2: pH = 3, [TiO2] = 30 mg/L and T = 25 °C, and for UV/H2O2: pH = 3, [H2O2]0 = 350 mg/L and T = 25 °C. After 60 min of irradiation time, the degradation efficiency, pseudo first order rate constant and operational cost value for the UV/TiO2 and UV/H2O2 processes were as 98.9%, 0.0771 min−1, 11.6

/m3 and 96.3%, 0.0573 min−1, 11.8

/m3 respectively. Also, thermodynamic parameters of activation energy, enthalpy change, entropy change and standard Gibbs free energy were calculated as 21.78 (kJ/mol), 19.37 (kJ/mol), −0.20 (kJ/mol K) and 73.34 (kJ/mol at 25 °C) for UV/TiO2 process and 7.62 (kJ/mol), 5.18 (kJ/mol), − 0.25 (kJ/mol K) and 80.14 (kJ/mol at 25 °C) for UV/H 2O2 process. The investigation also encompassed the exploration of 13 hybridization scenarios, including UV/TiO2/ H 2O2 and UV/H2O2/TiO2, revealing notable findings. Notably, a specific hybridization scenario, namely UV/TiO2 (30 mg/L)/ H 2O2(250 mg/L), demonstrated a significant synergistic effect (29.5%). Evaluating pollutant mineralization unveiled compelling results, with approximately 85% mineralization achieved after 90 min for the UV/TiO2(30 mg/L)/H2O2(250 mg/L) scenario, showcasing a remarkable synergism (44%) in the mineralization process.

Synthesis and photocatalytic properties of TiO2/BiVO4 nanocomposites and heterostructures

Thesis

Mar 2021

Drisya Karathuparathottathil Damodharan

This thesis presents the development of photoactive heterostructures of Bismuth vanadate (BiVO4) and Titanium dioxide (TiO2) and their application in photocatalysis under visible light irradiation, considering their abundance, non-toxicity, and high stability. The higher recombination rate in both materials, and the large band gap of TiO2 (3.2eV) limit their applications. Hence, band gap engineered TiO2/BiVO4 nanocomposites were synthesized by a modified Sol-gel method in the powder form with the stoichiometry of (1-x) TiO2: x BiVO4 (x= 0.2,0.8 &0.5) and another set with the low stoichiometry of BiVO4 ((100-x)%TiO2: xBiVO4); x= 0.5,1,1.5,2,2.5) was also synthesized considering the photocatalytic response from different contaminants. Considering their application in water treatment the powder was deposited as films using Radio-frequency sputtering. Films of two different architectures were developed: the first one is the composition of X=0.5 from sol- gel synthesized structures was chosen to make the target. And in the other, a layered heterostructure film with TiO2 layer over BiVO4 was deposited varying deposition time, power, chamber atmosphere and substrates. The optical, morphological, and electrochemical characterizations were performed. The UV-Visible characterizations confirmed the redshift in band gap depending on the stoichiometry of BiVO4 (≈2.4eV) and TiO2 (≈3.2eV). The X-ray diffractograms confirmed the formation of desired crystalline Monoclinic-BiVO4 (101, 103) and Anatase TiO2 (101) phases. The heterostructure formation was identified from TEM micrographs which clearly show the presence of junctions between planes. The electrochemical impedance spectroscopy corroborated the presence of surface states at the interface between the heterostructures causing higher charge separation efficiency within the structures which influenced the photocatalytic efficiency of the materials. A complete degradation of the organic dyes such as acid blue and methylene blue was observed using the powder structures within 20 minutes of irradiation. Arsenic (III) oxidation and removal was performed using Central Composite Design (CCD) by Response Surface Method (RSM) and a complete removal of Arsenic was observed within an hour of irradiation. The deposited films demonstrated near and above 90 % of organic dye degradation within 180 minutes of irradiation, among which the layered architecture was more efficient. The re-usability test results confirmed the stability of the films without much reduction in their performance.

Cluster Origin of Solvation Features of C-Nanostructures in Organic Solvents

Chapter

Jan 2016

The existence of fullerenes, Single-Wall Carbon Nanocones (SWNCs), especially Nanohorns (SWNHs), Single-Wall Carbon Nanotube (SWNT) (CNT) (NT), NT-Fullerene Bud (NT-BUD), Nanographene (GR) and GR-Fullerene Bud (GR-BUD) in cluster form is discussed in organic solvents. Theories are developed based on columnlet, bundlet and droplet models describing size-distribution functions. The phenomena present a unified explanation in the columnlet model in which free energy of cluster-involved GR comes from its volume, proportional to number of molecules n in cluster. Columnlet model enables describing distribution function of GR stacks by size. From geometrical considerations, columnlet (GR/GR-BUD), bundlet (SWNT/NT-BUD) and droplet (fullerene) models predict dissimilar behaviours. Interaction-energy parameters are derived from C60. An NT-BUD behaviour or further is expected. Solubility decays with temperature result smaller for GR/GR-BUD than SWNT/NT-BUD than C60 in agreement with lesser numbers of units in clusters. Discrepancy between experimental data of the heat of solution of fullerenes, CNT/NT-BUDs and GR/GR-BUDs is ascribed to the sharp concentration dependence of the heat of solution. Diffusion coefficient drops with temperature result greater for GR/GR-BUD than SWNT/NT-BUD than C60 corresponding to lesser number of units in clusters. Aggregates (C60)13, SWNT/NT-BUD7 and GR/GR-BUD3 are representative of droplet, bundlet and columnlet models.

Bundlet Model for Single-Wall Carbon Nanotubes, Nanocones and Nanohorns

Chapter

Jan 2013

This paper discusses the existence of single-wall carbon nanocones (SWNCs), especially nanohorns (SWNHs), in organic solvents in the form of clusters. A theory is developed based on a bundlet model describing their distribution function by size. Phenomena have a unified explanation in bundlet model in which free energy of an SWNC, involved in a cluster, is combined from two components: a volume one, proportional to number of molecules n in a cluster, and a surface one proportional to n1/2. Bundlet model enables describing distribution function of SWNC clusters by size. From purely geometrical differences, bundlet (SWNCs) and droplet (fullerene) models predict different behaviours. The SWNCs of various disclinations are investigated via energetic–structural analyses. Several SWNC’s terminations are studied, which are different among one another because of type of closing structure and arrangement. The packing efficiencies and interaction-energy parameters of SWNCs/SWNHs are intermediate between fullerene and single-wall carbon nanotube (SWNT) clusters; an in-between behaviour is expected. However, the properties of SWNCs, especially SWNHs, are calculated close to SWNTs. The structural asymmetry in the different SWNCs, entirely characterized by their cone angle, distinguishes the properties of some, such as P2.

Cluster Origin of Solvent Features of Fullerenes, Single-Wall Carbon Nanotubes, Nanocones, and Nanohorns

Chapter

Jan 2012

This chapter discusses the existence of single-wall carbon nanocones (SWNCs), especially nanohorns (SWNHs) in organic solvents in the form of clusters. A theory is developed based on a bundlet model describing their distribution function by size. Phenomena have a unified explanation in bundlet model in which free energy of an SWNC, involved in a cluster, is combined from two components: a volume one, proportional to number of molecules n in a cluster, and a surface one proportional to n1/2. A bundlet model enables describing distribution function of SWNC clusters by size. From purely geometrical differences, bundlet (SWNCs) and droplet (fullerene) models predict different behaviours. The SWNCs of various disclinations are investigated via energetic–structural analyses. Several SWNC’s terminations are studied which are different among one another because of the type of closing structure and arrangement. Packing efficiencies and interaction-energy parameters of SWNCs/SWNHs are intermediate between fullerene and single-wall carbon nanotube (SWNT) clusters.

Photocatalytic degradation of 4-nitrophenol in aqueous TiO2 suspensions: Theoretical prediction of the intermediates

Article

Full-text available

Jan 2002

The kinetics of the photocatalytic degradation of 4-nitrophenol (4-NP) in the presence of TiO2 has been investigated experimentally and theoretically. The effects of the catalyst loading, the initial concentration of 4-NP, H2O2 and the added Cu2+ ions on the degradation rate have been examined. A pseudo-first order kinetic model has been used to describe the results. A linear dependence of the rate constant upon the reciprocal of the initial 4-NP concentration has been obtained. The addition of H2O2 increases the reaction rate while Cu2+ ions has a detrimental effect. With the intention of predicting the primary intermediates, geometry optimizations of the reactants, the products and the transition state complexes have been performed with the semi-empirical PM3 method. The molecular orbital calculations have been carried out by an SCF method using RHF or UHF formalisms. Based on the results of the quantum mechanical calculations, the rate constants of the two possible reaction paths have been calculated by means of the transition state theory, and 1,2-dihydroxy-4-nitro-cyclohexadienyl radical which then forms 4-nitrocatechol has been determined as the most probable primary intermediate by the application of three different theoretical shortcut methods.

Photocatalysis in a Novel Semiconducting Optical Fiber Monolith Reactor for Wastewater Treatment

Article

Jan 2005

Hongfei Lin

An Overview of Semiconductor Photocatalysis

Article

Jul 1997
J PHOTOCH PHOTOBIO A

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

Decolourisation effects of Vat Green 01 textile dye and textile wastewater using H 2O 2/UV process

Article

Feb 2007
J PHOTOCH PHOTOBIO A

Wastewaters from textile industry contain various pollutants including a high content of organic matter, surfactants, additives and dyes. Dyes have obtained notoriety as hazardous substances, because most of them are toxic and considered to be resistant to biodegradation. Recently, advanced oxidation processes (AOP) have received considerable attention because it is possible to degrade organic compounds and colour from wastewaters. The decolourisation of Vat Green 01 textile dyestuff and real textile wastewater was investigated using UV radiation in the presence of H2O2 as function of pH, hydrogen peroxide concentration and dye concentration (in the study with the dyestuff). The results showed that the degradation increases as the initial H2O2 concentration increased up to a certain point at which hydrogen peroxide inhibited the wastewater photolytic degradation. The decolourisation rate follows pseudo-first order kinetic with the respect to the dye concentration.

Photocatalytic degradation of 4-nitrophenol in aqueous TiO2 suspensions: Theoretical prediction of the intermediates

Article

Jan 2002
J PHOTOCH PHOTOBIO A

The kinetics of the photocatalytic degradation of 4-nitrophenol (4-NP) in the presence of TiO2 has been investigated experimentally and theoretically. The effects of the catalyst loading, the initial concentration of 4-NP, H2O2 and the added Cu2+ ions on the degradation rate have been examined. A pseudo-first order kinetic model has been used to describe the results. A linear dependence of the rate constant upon the reciprocal of the initial 4-NP concentration has been obtained. The addition of H2O2 increases the reaction rate while Cu2+ ions has a detrimental effect.With the intention of predicting the primary intermediates, geometry optimizations of the reactants, the products and the transition state complexes have been performed with the semi-empirical PM3 method. The molecular orbital calculations have been carried out by an SCF method using RHF or UHF formalisms. Based on the results of the quantum mechanical calculations, the rate constants of the two possible reaction paths have been calculated by means of the transition state theory, and 1,2-dihydroxy-4-nitro-cyclohexadienyl radical which then forms 4-nitrocatechol has been determined as the most probable primary intermediate by the application of three different theoretical shortcut methods.

Photochemical Process for Water Treatment

Article

Apr 1993

Role of oxidative and reductive pathways in the photocatalytic degradation of organic compounds

Article

Jun 1999
COLLOID SURFACE A

The recent studies of concurrent oxidative and reductive processes occurring in the photocatalytic treatment are reviewed mainly focusing on the fate of carbon and nitrogen in the presence/absence of oxygen. The unusual possibility of photocatalysis to achieve degradation of organic compounds by concurrent reductive and oxidative reactions is discussed using the average oxidation numbers of C and N in the system. The effects of their initial values and of the nature of the organic substrate are outlined.

Decolorization of Textile Industry Wastewater by Photo Catalytic Degradation Process

Article

May 2001
DYES PIGMENTS

The photocatalytic degradation of various dyes (Orange II, Orange G, Congo Red, Indigo Carmine, Crystal Violet, Malachite Green, Remazol Blue and Methyl Yellow) has been studied, using P25 Degussa as catalyst. All dye solutions underwent a decolourization. The kinetics of reaction have been studied and were found to be zero or first order with respect to the dyes. This was compared with the adsorption properties. The effect of the addition of hydrogen peroxide has been studied. An enhancement of the rate has been observed in all cases and the order with respect to the additive was found to be almost zero. It is difficult to give a general picture of the kinetics using these very different dyes but the process was found to be effective for the decolourization of textile wastewater.

Kinetics of Photocatalytic Degradation of Reactive Dyes in a TiO2 Slurry Reactor

Article

Jun 2002
J PHOTOCH PHOTOBIO A

The textile industry consumes considerable amounts of water during the dyeing and finishing operations. Dyes are extensively used and hence wastewaters discharged in rivers or public sewage treatment plants are highly contaminated. In this work, a detailed investigation of the adsorption and photocatalytic degradation of the safira HEXL dye, an anionic azo dye of reactive class, is presented. H2O2 and UV light have a negligible effect when they are used on their own. The adsorption of dye on the semiconductor shows a strong dependence on the pH and follows a Langmuir adsorption model. The photodegradation kinetics is discussed in terms of the Langmuir–Hinshelwood model.The effect of pH, amount of photocatalyst, UV light intensity and hydrogen peroxide concentration is discussed. The relative photonic efficiency of the system is reported using phenol as a standard organic compound.

Enhancement of the rate of solar photocatalytic mineralization of organic pollutants by inorganic oxidizing species

Article

Aug 1998
APPL CATAL B-ENVIRON

Particulate suspensions of TiO2 irradiated with natural solar light in a large experimental plant catalyze the oxidation of a typical organic contaminant: pentachlorophenol (PCP). The addition of oxidants, concentration of which is kept constant during treatment, such as hydrogen peroxide, peroxymonosulphate (oxone) and peroxydisulphate increases the rate of photodegradation of PCP in the following order: S2O2−8>Oxone>H2O2. Peroxydisulphate (10 mM), selected as the best oxidant studied, has been applied to the development of a solar photocatalytic plant for the treatment of commercial pesticide rinsates found in the wastewater produced by a pesticide container recycling plant, which includes the correct treatment of this highly contaminating effluent. The first results, without process or hardware optimisation, show that peroxydisulphate enhances the photocatalytic mineralization rate at least five times.