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Surfactant-Free Green Synthesis of ZnS QDs with Active Surface Defects for Selective Nanomolar Oxalic Acid Colorimetric Sensors at Room Temperature
Abstract
Synthesis of quantum dots (QDs) uses surfactants to enable its applications viable with minimum surface defects. The environmental benign method without a surfactant is a way forward for sustainable applications. Sunlight mediated synthesis of uniform ZnS QDs without a surfactant is achieved with pristine surface defects that facilitate visible light absorption. The cubic phase of QD and size are revealed using the transmission electron microscope and X-ray diffraction studies. The unique absorption property is utilized to demonstrate a cost-effective colorimetric sensor for biological toxic substances, oxalic acid using absorption spectroscopy. The unparalleled performance among the enzymatic or non-enzymatic processes for oxalic acid detection is realized, however, without any noble metal, for a wide range of 1 nM to 0.5 mM concentrations with a limit of detection of 0.2 nM. Typical inferences from organic acids, water-soluble salts, and metal ions are also investigated. Further, the role of surface defects in QDs is unfurled with photoluminescence, infrared, and Raman spectroscopic measurements, and the underlying mechanism of OA detection is elaborated. Thus, green synthesis and unmasking the influence of surface defects in ZnS QDs as demonstrated for selective detection open up for various other applications like solar cell, catalyst.
... Importantly, theoretical photocarrier generation efficiency of ZnS was reported to be better than the widely used TiO 2 photocatalyst [21,22]. ZnS is a direct band semiconductor with bandgap energies of 3.6 and 3.8 eV for sphalerite and wurtzite crystal phases, respectively at room temperature [23][24][25]. Due to rich morphologies at the nanoscale with regards to polar surfaces, thermal and chemical stability, high electronic mobility, and low toxicity, it is regarded as a cost-effective environmental-friendly catalyst [19,[26][27][28]. For the maximum benefits, photocatalysts are expected to perform in the whole solar spectral range including the most abundant visible part. ...
... Beyond the vacancy defects, the elemental type sulfur defect (E s ) in the pristine ZnS creates a band around 2.3 eV which then overhauls the significant visible light absorption [23,24]. Notably, it is rarely investigated for the study of photocatalysis. ...
... Notably, blue-shifted band gap values are observed for ZnS-A and ZnS-B due to the quantum confinement size effect. The quantum regime sizes are well supported by the structural study (Fig. S1) as well as from the particle size deduction by using the Brus equation [23,45]. However, the most striking feature in the UV-Vis absorption spectra is the presence of novel broad feature in the visible region. ...
... Importantly, theoretical photocarrier generation efficiency of ZnS was reported to be better than the widely used TiO 2 photocatalyst [21,22]. ZnS is a direct band semiconductor with bandgap energies of 3.6 and 3.8 eV for sphalerite and wurtzite crystal phases, respectively at room temperature [23][24][25]. Due to rich morphologies at the nanoscale with regards to polar surfaces, thermal and chemical stability, high electronic mobility, and low toxicity, it is regarded as a cost-effective environmental-friendly catalyst [19,[26][27][28]. For the maximum benefits, photocatalysts are expected to perform in the whole solar spectral range including the most abundant visible part. ...
... Beyond the vacancy defects, the elemental type sulfur defect (E s ) in the pristine ZnS creates a band around 2.3 eV which then overhauls the significant visible light absorption [23,24]. Notably, it is rarely investigated for the study of photocatalysis. ...
... Notably, blue-shifted band gap values are observed for ZnS-A and ZnS-B due to the quantum confinement size effect. The quantum regime sizes are well supported by the structural study (Fig. S1) as well as from the particle size deduction by using the Brus equation [23,45]. However, the most striking feature in the UV-Vis absorption spectra is the presence of novel broad feature in the visible region. ...
Sustainable pollutants remedial is focussed by using surfactant-free ZnS nanoparticles (NPs) which are decorated with elemental-type sulfur defects (E s). Such functional ZnS NPs enable complete and rapid degradations of dye, drug (paracetamol, tetracycline), and explosive (trinitro-phenol) with UV to visible light irradiations. The evi-dences of E s formation are established by XPS, PL, and chemical reaction studies. HRTEM, XRD, EELS, UV-vis. absorption, PL, and Raman measurements have provided structural details of nanoparticles as well as confirmation on the critical role of E s towards the harvest of visible light. The highest carrier lifetime (5.8 µSec) of E s with a huge photocurrent (1.4 µA/cm 2) has revealed further insights of the exceptional degradation abilities of ZnS nanocatalysts of pollutants. The nanocatalyst decays pollutants completely under direct sunlight and shows~24 and~2.5 times better performances than the commercial ZnS and TiO 2 (P25), respectively. Thus, impeccable photocatalysis efficacy of defects decorated ZnS nanocatalysts under a wide range of wavelengths of light is demonstrated. The study opens up further energy harvesting applications.
... emitting diodes, electroluminescence, flat panel displays, infrared windows, sensors, lasers, and biodevices. [4][5][6] Besides, it is a photocatalytic material of immense significance thanks to its brilliant optical properties, especially in the nano regime. 3,4 Surface engineering allowing control on surface reactivity and tuning of optoelectronic properties is of considerable research interest. ...
... 23 Defects in the ZnS NPs introduce new inter energy levels to accomplish the light absorption. 6 On adsorption of light, these defects sites participate in carrier generation and transfer as well as prevent the recombination of photogenerated charge carriers. 4,10,24 Thus, control of their types and density for energy conservation is of utmost importance. ...
Energy-efficient and environmentally benign photocatalyst with enormous reaction sites activated by similar wide spectrum of sunlight to treat an aqueous dye pollutant is of contemporary research interest. At the onset, an energy-friendly microwave radiation process is used to ascertain the single-step growth of 4 nm cubic ZnS quantum dots (QDs) without a capping agent. These QDs characterized structurally by XRD, HRTEM, and EELS technique holds unique optical properties like strong visible light absorption due to defects, quantum confinement effect, and bandgap energy value are evaluated using the UV-Vis and photoluminescence measurements. Photocatalytic studies with methylene blue and methylene orange dyes with exposures to UV and visible light sources are approached to unfurl the efficacy of ZnS QDs and understand the pertinent mechanisms. First-time complete degradations of both dyes in record low time under visible light irradiation are obtained, primarily due to large surface defects in the pristine ZnS QDs. Furthermore, the fastest degradation of 10 ppm dye in 20 minutes with UV-C source is successfully demonstrated. The technical importance with in-depth insights of the photocatalytic mechanism with the resonance and the non-resonance energies of the bandgap value of ZnS QD is elaborated. Recyclability of the photocatalyst is ascertained clearly up to 3rd cycles. Thus, the efficacy of these ZnS stands to be most competent amongst other reports.
... The band gap was found to be 3.99 eV. There was a blue shift compared to the bang gap of bulk ZnS (E g = 3.6 eV), which is caused by quantum confinement of charge carriers [48][49][50]. ...
... One way is to achieve green and lowcost synthesis. More and more researchers have made efforts after realizing this problem, with a good deal of works about green synthesis have been done (Rajput, 2018;Liu et al., 2017c;Juine and Das, 2020;Yu et al., 2020a;Filippo et al., 2013;Farrokhnia et al., 2017). The other way is to develop degradable and recyclable sensing materials (Wongniramaikul et al., 2018;He et al., 2005;Kim et al., 2018;Mettakoonpitak et al., 2021;Sani et al., 2021), which largely reduce pollution and protect the environment. ...
Detection of heavy metal ions has drawn significant attention in environmental and food area due to their threats to the human health and ecosystem. Colorimetry is one of the most frequently-used methods for the detection of heavy metal ions owing to its simplicity, easy operation and rapid on-site detection. The development of chromogenic materials and their sensing mechanisms are the key research direction in the area of colorimetric method. Since each chromogenic material has their unique optical and chemical properties, they have totally different colorimetric sensing mechanisms. This review focuses on the chromogenic materials and their sensing strategies for the colorimetric detection of heavy metal ions. We divide the chromogenic materials into three types, including organic materials, inorganic materials, and other materials. As for each type of chromogenic material, we discuss their detailed sensing strategies, sensing performance, and real sample applications. Moreover, current challenges and perspectives related to the colorimetry of heavy metal ions are also discussed in this review. The aim of this review is to help readers to better understand the principles of colorimetric methods for heavy metal ions and push the development of rapid detection of heavy metal ions.
... As shown in Fig. 5A1 and B1, the band gap energy is calculated by extrapolating the tangent of the near edge band, yielding E g = 5.05 eV and E g = 5.00 eV for MPA-ZnS QDs and MPS-ZnS QDs respectively. It is observed that the optical band gaps are larger than that of bulk ZnS (3.6 eV) due to quantum confinement effect [29,42,43]. The E g of the X-capped ZnS QDs has been calculated in order to estimate their particle size by using the Brus equation [32] (Eq. ...
X–ZnS quantum dots (QDs) are synthesized in aqueous solution by a simple aqueous chemical route where X represents 3-mercaptopropionic acid (MPA) or 3-mercapto-1-propanesulfonic acid (MPS) which are two well-known low cost and stable ligands. The synthesized X–ZnS QDs yielded aqueous suspensions of nanoparticles with excellent monodispersity, water solubility and fluorescence stability with a relatively high fluorescence quantum yield of 11% and 10% for MPA-ZnS QDs and MPS-ZnS QDs respectively. Under optimal conditions, the prepared X–ZnS QDs are used to detect tetracycline (TC) based on their fluorescence quenching induced by the target analyte via electrostatic interaction. The Stern–Volmer-type equation has been fitted to the quenching curve of each QDs, from which MPA-ZnS QDs has shown a larger linear range and a lower limit of detection than MPS-ZnS QDs. The fluorescence response of MPA-ZnS QDs is linearly with respect to TC concentration over a wide range from 200 nM to 6000 nM with a detection limit of 30 pM. The combination of non-toxicity, simplicity and low cost together with high analytical performance of the proposed MPA-ZnS QDs make it promising for the determination of trace TC in food products of animal origin.
The frequent emergence of viral infectious diseases and their acute effects on public health and the world economy has pushed the boundaries of current science and technologies. The convergence of nanotechnology with virology has opened multiple windows for different applications in biomedical and environmental sciences related to the virus. The use of various nanoparticles and their conjugates is important in diagnostics and treatment of viral diseases. This review explores the translational potential of zinc oxide (ZnO) nanoparticles in virus detection techniques and methodologies with comparative scrutiny of the time-consuming nature and limitations of traditional methods. It highlights the acuteness of viral diseases by illustrating the mechanistic pathogenesis of different virus types and underscores the need for rapid and accurate diagnostic techniques. The study entails the advantages of ZnO NPs over traditional diagnostic methods in both clinical and research settings addressing profusely different issues like false negative and positive signals. Challenges and future directions are sightseen entailing the optimization, sensitivity, and integration of ZnO NP-based diagnostics with existing platforms. The study illuminates the intricate amalgamation of nanotechnology with virology for the development of innovative diagnostic techniques as a promise to reshape the diagnostics and management of the disease.
Single‐phase zinc sulphide (ZnS) quantum dots are synthesized by the hydrothermal method without using any capping agent. XRD, TEM, UV‐Visible spectroscopy are used to characterize the structure, size, surface states, and photoluminescence properties of ZnS quantum dots for the application as a fluorescence sensor. Fluorescent sensors are widely utilized for the detection of biomolecules or metal ions due to their high sensitivity, high specificity, immunity to light scattering, and ease of operation. Cadmium is used as a fluorescence super quencher to detect the presence of cadmium. The relative integrated emission intensity of ZnS quantum dots decreases as the amount of Cd increases. A strong broad band cantered at about 320 nm is observed in the excitation spectrum of ZnS quantum dots. Their emission spectrum, peaking at about 408 nm, is due mostly to the trap‐state emission. The 408nm emitted radiation is then used to detect the presence of fluoranthene, a potential carcinogen, present in the solution, and it is found that ZnS quantum dots prepared can effectively act as a sensor to sense the presence of fluoranthene. The novelty of the process is the use of water as a solvent for synthesis without using any capping agent by a slow hydrothermal process. image
Global concerns have been excited by burgeoning electromagnetic pollution and climate change. Paying attention to building materials is one of the best ways to refine electromagnetic pollution and save energy. Herein, a practical nanocomposite has been introduced that not only absorbs microwaves, but also plays a significant role in energy‐saving. Interestingly, the approach related to the selection of a simple experimental procedure, cost‐effective substrates, and building matrix develops the practical applications of the eventual product. Initially, graphite‐like carbon nitride (g‐C3N4) nanosheets are tailored using a conventional sintering route, and then the prepared nanosheets are ornamented by zinc sulfide (ZnS) nanoparticles through a facile hydrothermal scenario. Remarkably, the microwave and optical features of the tailored ZnS/g‐C3N4 nanocomposite are modulated by regulating the mass fraction of ZnS into 2D structures. Interestingly, a novel defecting agent is used to boost the dielectric characteristics of g‐C3N4 through an innovative complementary hydrothermal and combustion scenario. Eventually, the architected structures are blended with gypsum plaster to evaluate energy‐saving and microwave‐absorbing performance. The nanocomposites fabricated by ZnS/defected g‐C3N4/gypsum plaster as building materials have significant microwave‐absorbing and infrared reflection capacity. The presented research opens a new vista for simultaneous development of advanced functional materials for energy‐saving and microwave absorption.
The controlled release strategy can make the constructed sensor have the function of self-on/off, which has an obvious effect on improving the sensitivity in immunoassays. Metal organic gels (MOGs) are the most noteworthy. They are materials with ultrahigh surface area, highly dispersed atomical metal sites, and well-defined porosity and can be used as an efficient luminophore to cause the developed sensor to have good hydrophilicity and adjustability, thus further improving the detection sensitivity. In this work, a novel on/off electrochemiluminescence (ECL) gel aptasensor was constructed using the Cys-[Ru(dcbpy)3]2+ gel as a luminophore, ZnS quantum dots (QDs) as quenchers, and aminated mesoporous silica nanocontainers (SiO2-NH2) as carriers of controlled release for prostate specific antigen (PSA) detection. Specifically, the ssDNA and PSA aptamer made up clamp-like molecules to block holes of the SiO2-NH2 after encapsulating the quencher ZnS QDs. Because of the specific binding between the PSA antigen and aptamer, the clamp-like molecules of ssDNA and the PSA aptamer were disassembled. Finally, the release of ZnS QDs was triggered, thereby realizing a self-off mode of the ECL signals under a co-reactant-free environment by ECL resonance energy transfer (ECL-RET) between the Cys-[Ru(dcbpy)3]2+ and ZnS QDs. In addition, the quenching mechanism was confirmed by molecular orbitals from the theoretical calculation level. The detection limit of the gel aptasensor for PSA was as low as 1.01 fg/mL, showing excellent sensitivity and accuracy. These strategies provided a feasible idea for PSA and even other tumor marker immunoassays.
Since oxalate plays an important role in the metabolic assessment of urolithiasis, there is need for convenient and efficient methods for oxalate detection. Herein, we report a three-signal fluorescence strategy for oxalate analysis based on the ability of oxalate to reduce Cu²⁺ to Cu⁺, and the ability of pyrophosphate-cerium coordination polymeric networks (PPi-Ce CPNs), cadmium telluride quantum dots (CdTe QDs), and N-Methyl Mesoporphyrin (NMM) to selectively detect Cu²⁺ and Cu⁺. The detection range was 100 nM to 1 mM, the turnaround time was 6 min, while the limits of detections for PPi-Ce CPNs, QDs and NMM as reporters were 25 nM, 10 nM and 40 nM, respectively. Visual detection of oxalate relied on color change in the solution, which could be observed using the naked eye. The fluorescent system was used for oxalate analysis in 44 urine samples (32 calcium oxalate stone patients, 12 controls without urolithiasis), and the results were consistent with clinical diagnosis and imaging data. Moreover, the visual system was used to analyze 8 urine samples (4 patients and 4 controls), and showed good consistency with clinical diagnosis and computed tomography imaging results. These findings suggest that the method has potential application for the metabolic assessment of urolithiasis.
Although some detection methods for oxalic acid have been reported, the rapid, simple and on-site detection on oxalic acid was rarely presented. In this work, a “turn-on” fluorescence sensor for oxalic acid was realized by the simple and on-site procedure in aqueous media. A tetra-cyanostilbene macrocycle was synthesized by simple “2 + 2” condensation in 72 % yield. It displayed the strong “turn-on” blue fluorescence on selectively detecting oxalic acid among various ions and biomolecules. It possessed the high sensing sensitiveness with the detection limit of 3.82 × 10⁻⁶ M. The sensing mechanism was clarified by pH influence on complexation, fluorescence Jobs’ plot, MS spectra, and ¹H NMR spectra, confirming that non-dissociated oxalic acid was bound in the cavity of the macrocycle based on hydrogen bonds. This sensing ability for oxalic acid was successfully applied in test paper, on-site detection for real samples of taros and rust treatment, suggesting the good application prospect in the rapid, simple and on-site detection for oxalic acid in daily life and industry.
Zinc sulfide (ZnS) nanoparticles (NPs) are potentially useful in various fields such as catalysis, electronics, biomedical, etc. Two important practices which are primarily followed for the synthesis of ZnS NPs are chemical and physical techniques. However, both these techniques are expensive, and more importantly, these processes produce toxic NPs for which the biological and medicinal applications of these NPs find difficulty. In consequence, the biological method (green synthesis) has recently been adopted as an expedient alternative to generate ZnS NPs with higher stability, as this approach is economical, eco-friendly and non-toxic and it includes plant extracts, microorganisms, etc. The present review focuses on the discussion of different green synthetic approaches of ZnS NPs using plant extract, microorganism and other natural products. Besides, a brief description on antimicrobial activities of ZnS NPs has been presented. The findings from this review can suggest a feasible use of plant's extract and microorganisms as a tool for the synthesis of ZnS nanoparticles.
Nanomaterials are important class of materials due to their size and shape-dependent properties as compared to bulk materials. As a result, nanomaterials are increasingly interested in the technological applications of fundamental research. Among these semiconductor quantum dots (QDs) are a significant class of nanomaterials. Zinc Sulfide (ZnS) is an important semiconductor belongs to II–VI group in periodic table, a wide bandgap semiconductor, bulk energy gap 3.6 eV, with exciton binding energy of 39 meV, which is easily synthesizable material and chemically stable as compared to other chalcogenides and hence many research pronounced on zinc sulfide. Herein, we report the synthesized of Zinc Sulfide QDs by the chemical precipitation method using thioglycolic acid (TGA) as a capping agent and hydrazine hydrate-sulphur complex plays a vital role in the growth ZnS QDs. The synthesized ZnS QDs were characterized using UV–visible absorption spectroscopy, photoluminescence spectroscopy (PL) , XRD, FTIR, SEM and TEM. To support the formation of ZnS QDs, XRD spectrum results the arrangement of ZnS in the cubic crystal system. The estimated particle size is 2.62 nm. The ZnS QDs are stable, fluorescent and spherical in shape as noted by the results of the PL spectral analysis and TEM images. The produced ZnS QDs are amorphous in nature and can be used in the applications like sensors, Field Emitting Diodes (FET), electroluminescence, flat panel displays and photocatalysis.
Metal oxide nanoparticles (MONs) emerged as antimicrobials due to the occurrence of multidrug-resistant (MDR) bacterial strains. Antimicrobial activity has been shown to be influenced by the route of synthesis and precursors. Hence, a plethora of literature exists on prominent MONs like Ag2O, CuO, ZnO, TiO2, MgO, Al2O3, and Au, as activity was influenced by physicochemical parameters which are influenced vis-a-vis by new synthesis methods. Conventionally or controversially, researchers looking for antimicrobial activity still predominantly conduct testing on planktonic cells irrespective of application. It is now evident that microbes follow a biofilm mode of living. However, an outcome from these revealed that the actions of MONs were strain specific and dependent on positive charge of NP with smaller size, demonstrating better bactericidal effects. No given NP has been shown to exhibit a broad-spectrum activity under in situ conditions at low concentrations, which is a prerequisite for successful development as a product for environmental/public hygiene applications. This trigged the testing of polymetallic oxide (PMNO)/bimetallic nanoparticles toward broad-spectrum activity which indeed was more effective. Again these evaluations were restricted to individual strains and not at the community level. Biofilms are the preferred mode for most microbes, and biofilm formation is ubiquitous and a surface-associated phenomenon. Control measures should therefore aim at eliminating biofilms, which also serve as a reservoir of microbes. In-lieu of these, realizations have fuelled new research, like using NP as nanofillers, surface immobilization of NP into different polymeric substrates for varied applications. Currently, polymer nanocomposites and surface modifications are the mainstay, and a paradigm shift in studies testing these formulations for inhibition of biofilm formation has resulted in the development of several new antibiofilm and antifouling coating formulations.KeywordsCuOZnOTiO2AntibacterialBiofilmsAntifouling coatingsPolymer nanocompositesROSOxidative stress
S. aureus
E. coli
P. aeruginosa
The aimlessness in the selection of dielectric absorbing materials and the regulation of complex permittivity consumes time and resources. It is an effective way to construct electromagnetic wave (EMW)-absorbing materials dominated by dielectric loss to select materials and adjust complex permittivity based on theory. With sulfide as an example, a hollow ZnO/ZnS composite was constructed using ZnO as a hard template. Subsequently, based on the diverse binding ability of Cu and Zn ions to S ions, the compositions, interfaces, and defects of the sample were simultaneously regulated. There was competition and synergy between the relaxation process caused by the defects and interfaces and the conductivity loss, resulting in the regulation of complex permittivity. Furthermore, the hollow structure effectively reduced the density of the material and improved the impedance matching ability of the sample. As a result, the effective absorption bandwidth (EAB) of the hollow nanoflower ZnO/ZnS/CuS composite reached 5.2 GHz (from 12.8 to 18 GHz) with a matching thickness of 1.59 mm. This method provides a direction for ameliorating the complex permittivity of EMW-absorbing materials dominated by dielectric loss to realize broadband absorption.
The chemical transformation from zinc oxide (ZnO) to zinc sulphide (ZnS), using di-tert-butyl disulphide (TBDS) as a highly reactive sulphur precursor, is demonstrated herein. Through anion exchange, we investigate the phase and morphological changes associated with the nanoparticle (NP) transformation of ZnO to ZnS using TBDS. The Zn–O–S alloy was not formed through the anion exchange reaction, only the ZnO and ZnS phases were detected. The NPs were transformed from a solid sphere to a hollow structure, induced by the nanoscale Kirkendall effect. Even with the dramatic shape and phase changes occurring in the NPs, the Zn oxidation state remained as 2+ throughout the 2 h anion exchange reaction. In addition, trioctylphosphine (TOP), a soft base ligand, increased the anion exchange reaction rate, facilitating the reaction with TBDS. Furthermore, anion exchange with elemental sulphur required a longer reaction time (3 h) than that with TBDS (2 h). Consequently, this study offers not only insights into phase and morphological transformations by anion exchange, but also the advantages of utilizing TBDS as a sulphur precursor.
The Internet of Things (IoT) has limitless possibilities for applications in the entire spectrum of our daily lives, from healthcare to automobiles to public safety. The IoT is expected to grow into a trillion dollar industry worldwide over the next decade. The components of the IoT will be integrated with cloud computing, which will facilitate easy access and analysis of big data stored in cloud systems across the globe. Radio frequency identification (RFID) technology is based on wireless communication systems and offers easy integration into the Internet cloud system. The potential of RFID tag sensor technologies has been studied in different industrial sectors including healthcare, food safety, environmental pollution, anti-counterfeiting of bank-notes and fake medicines, factories, customer shopping behavior, logistics, public transport, and safety. In this review article, the role of inkjet-printed RFID tag sensors is described in the emerging fields of IoT and the Internet of Nano Things (IoNT). This review is concerned with the use of inkjet-printed nanomaterials to fabricate RFID-enabled devices as a component of IoT technology. Inkjet-printed flexible RFID tag sensors based on nanomaterials including multilayer graphene, carbon nanotubes, gold, silver and copper nanoparticles, conductive polymers and their based composites used for detecting toxic gases and chemicals are discussed. Inkjet-printed nanomaterial-based RFID tag sensors that can be easily printed on flexible paper, plastic, textile, glass, and metallic surfaces, show potential in flexible and wearable electronics technologies. Finally, challenges such as energy and safety issues for RFID tag sensors are analyzed.
An enzyme-free oxalic acid (OA) electrochemical sensor was assembled on indium tin oxide (ITO) plate on which a film of laponite ionogel was coated that resulted in an L/IL/ITO electrode. This ionogel electrode was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and UV–Vis spectroscopy techniques. Electrochemical oxidation of OA on the electrode surface was investigated by cyclic voltammetry. Further this electrode exhibited high electrochemical activity that yielded well-defined peaks of OA oxidation, and a notably suppressed over-potential compared to the laponite–ITO (L/ITO) electrode. Under optimized conditions, a good linear response (anodic current) was observed for the OA concentration in the 1–20 mM range with a detection limit of 3 μM. Furthermore, this electrochemical strip sensor presented good characteristics in terms of stability, and reproducibility offering promise of applicability of this green sensor platform.
A simple one-step method was designed for the first time to produce a novel Zn(II) dithiocarbamate/ZnS nanocomposite. The developed Zn(II) dithiocarbamate/ZnS nanocomposite was found to exhibit outstanding performance on Cr⁶⁺ removal from aqueous solutions and the removal rate could reach more than 98% in just a few seconds. Various influencing factors such as the addition quantity, pH value and reaction temperature were investigated in order to determine the optimal removal conditions. It was shown that the Cr⁶⁺ removal ability of the Zn(II) dithiocarbamate/ZnS nanocomposite remained high at almost all the pH values and the degradation rate increased gradually with the reaction temperature up to 323 K. Compared to the traditional catalysts, which usually involve a complex production process with a high cost and a low degradation rate, the novel Zn(II) dithiocarbamate/ZnS nanocomposite has great potential in applications for wastewater treatment.
Amostras de ZnS dopadas com Mn com formula de composição Zn1-xMnxS, x = 0, 0,02, 0,05 e 0,10 foram preparadas por método químico. As amostras foram caracterizadas pelas propriedades estruturais, morfológicas e óptica por difração de raios X (DRX), microscopia eletrônica de transmissão (MET), espectroscopia de infravermelho com transformada de Fourier (FTIR) e espectrometria UV-vis. Difratogramas de DRX confirmaram a estrutura cúbica do ZnS puro sem fases secundárias para o ZnS puro e dopado com Mn. O valor do parâmetro de rede aumenta um pouco com a concentração de Mn por causa da substituição de Mn na rede do ZnO. Imagens MET mostram que as partículas tem forma esférica com tamanho médio de partícula 3-4 nm. As espécies químicas dos cristais crescidos foram identificadas por FTIR. Os espectros de absorção óptica mostram a diminuição do gap de banda com o aumento da concentração de Mn.
A simple and reliable colorimetric method for the quantitative determination of citalopram (CIT) enantiomers in aqueous solution using gold nanoparticles as a colorimetric probe was presented. S-citalopram induced aggregation of citrate capped AuNPs resulted in a decrease in the plasmon absorption at 520 nm and the formation of a broadened surface plasmon band around 600–700 nm. The results show that the colorimetric system possesses a very well selectivity toward S-citalopram compare to the R-citalopram as evidenced by the fact that there is the same color change from S-citalopram and (RS)-citalopram, and significant UV–vis spectral shift. The experimental conditions were optimized and the results show that S-citalopram can be determined in a linear range 2.5 × 10−6–6.0 × 10−4 M with correlation coefficients of 0.9963 and limit of detection 2.1 × 10−6 M.
Egyptian dieticians typically rely on foreign databases to find out oxalate content of food due to unavailability of local databases. The soil, fertilizers, climate and cultivars are often very different. Therefore, the purpose of this study is to establish a local database of oxalate content in Egyptian grown fruits and vegetables and selected daily common herbs. The current study analysed the total and the soluble oxalate in 37 Egyptian grown fruits, vegetables and 9 commonly used herbs. Two methods were used for screening the Egyptian foods for oxalate concentration; the first method was AOAC 1999 and the second was enzymatic method. Total oxalate varied greatly among the vegetables examined, ranging from 4 to 917 mg/100 g F.W. Total oxalate of analysed fruits ranged from 9 to 50 mg/100 g F. W. There is a strong correlation found between the two methods used. Vegetables were classified into 4 categories; low oxalate concentration containing less than 10 mg of oxalic acid /100 g F.W., such as cabbage, courgette, cucumbers, garlic, spring onions and turnip. Moderate oxalate concentration vegetables containing 10-25 mg/100 g F. W., such as aubergine, field bean, corn, peppers and watercress. High oxalate concentration vegetables containing 26-99 mg/100g F.W., such as f?l, green beans, celery, mallow, okra and sweet potatoes. Very high oxalate concentration containing 100-900 mg/100g F.W. such as Swiss chard, molokhia, purslane and vine leaves (fresh). Extensive amounts of total oxalate (201-4014 mg/100 g D.W.) were found in daily common herbs such as caraway seed, green cardamom, cinnamon, coriander seeds, cumin, curry powder, ginger and turmeric powder.
The ferromagnetic mediation centers of enough high concentration are the prerequisites for the realization of ferromagnetic diluted magnetic semiconductors. Zn0.97Co0.03S ultrafine nanoparticles of diameter ˜4 nm with zinc blende structure were synthesized by the chemical coprecipitation method. After annealing in H2 atmosphere at 500 °C for 2 h, Zn0.97Co0.03S transformed to wurtzite structure of increased particle size and strongly enhanced room temperature ferromagnetism has been observed. The possible ferromagnetic contribution from metallic Co due to reduction by H2 has been excluded. Combining the structural characterizations and density functional theory calculations, we conclude that the interstitial H+ ions in wurtzite ZnS may provide efficient ferromagnetic mediation between the neighboring Co2+ ions.
We report, for the first time, the luminescence property of the hydroxyl group surface functionalized quantum dots (QDs) and nanoparticles (NPs) of SnO2 using low energy excitations of 2.54 eV (488 nm) and 2.42 eV (514.5 nm). This luminescence is in addition to generally observed luminescence from ?O? defects. The as-prepared SnO2 quantum dots (QDs) are annealed at different temperatures in ambient conditions to create varied NPs in size. Subsequently, average size of the NPs is calculated from the acoustic vibrations observed at low frequencies in the Raman spectra and by the transmission electron microscopic measurements. Detailed photoluminescence studies with 3.815 eV (325 nm) excitation reveal the nature of in-plane and bridging ?O? vacancies as well as adsorption and desorption occurred at different annealing temperatures. X-ray photoelectron spectroscopy studies also support this observation. Defect level related to the surface ?OH functional groups shows a broad luminescence peak around 1.96 eV in SnO2 NPs which is elaborated with the help of temperature dependent studies.
Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible light were evaluated by gas chromatograph, and the midgap states of ZnS introduced by S vacancies were examined by density functional calculations. Our study reveals that the concentration of S vacancies in the ZnS samples can be controlled by varying the amount of the reducing agent NaBH4 in the synthesis, and the prepared ZnS samples exhibit photocatalytic activity for H2 production under visible-light irradiation without loading noble metal. This photocatalytic activity of ZnS increases steadily with increasing the concentration of S vacancies until the latter reaches an optimum value. Our density functional calculations show that S vacancies generate midgap defect states in ZnS, which lead to visible-light absorption and responded.
Glutathione protected, silver clusters were synthesized within gel cavities, using sunlight. Compared to the conventional chemical reduction process, this method is cheaper and environment-friendly as it involves the use of natural resources. As-synthesized silver quantum clusters in aqueous medium shows distinct step-like behavior in its absorption profile. It has been characterized with various spectroscopic and microscopic techniques such as UV/Vis spectroscopy, luminescence spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), High Resolution Transmission Electron Microscopy (HRTEM), and X-ray Photoelectron Spectroscopy (XPS). Polyacrylamide gel cavities seemingly control the growth of the particles. Cluster synthesis is scalable by increasing the amount of reagents yielding hundreds of milligrams in a single step. Antibacterial property of the as-synthesized Ag clusters was studied against a gram negative organism, escherichia coli.
The microscopic properties of several ZnO and ZnS surfaces of low Miller index are investigated through first-principles calculation of the surface energy, crystal structure and electronic structure. Generally, the non-polar surfaces_such as (101̄0) and (112̄0) are found to be more stable than the polar (0001)-Zn surface. The (112̄0) surface is found to be the most stable for both ZnO and ZnS semiconductors and the (101̄0) surface is found to have a slightly larger surface energy. These are consistent with the abundant observations of ZnO nanostructures having (112̄0) and (101̄0) surfaces. The near-surface structures and electronic structures are discussed.
It has been reported that phase structure and surface polarity largely affect the photocatalytic efficiency of semiconductor nanostructures. To understand the chemical activity of ZnS at the electronic level, we investigate electron structures and carrier transportation ability for bulk intrinsic zinc blende (ZB) and wurtzite (WZ) ZnS, as well as the reaction pathway of hydrogen generation from water splitting on Zn- and S-terminated polar surfaces. The electron structure calculations prove that the WZ phase possesses a higher reducing ability than the ZB phase. The conductivity of the bulk ZB phase surpasses that of the WZ phase at or above room temperature. As the temperature increases, the asymptotic conductivity ratio of WZ/ZB is close to the Golden Ratio, 0.62. Reaction kinetics studies indicate that Zn-terminated polar surfaces are more chemically active than S-terminated polar surfaces in the reaction of hydrogen generation from water splitting. The calculation results suggest that the first H splitting from water on Zn-terminated polar surfaces can occur with ground state electronic structures, while photo-assistance is necessary for the first H splitting on the S-terminated surfaces. Electronic triplet states calculations further show that Zn-terminated surfaces are more photosensitive than S-terminated surfaces.
The first- and second-order Raman spectra of cubic ZnS (β-ZnS, zinc-blende) are revisited. We consider spectra measured with two laser lines for samples with different isotopic compositions, aiming at a definitive assignment of the observed Raman features and the mechanisms which determine the linewidth of the first order TO and LO Raman phonons. For this purpose, the dependence of the observed spectra on temperature and pressure is investigated. The linewidth of the TO phonons is found to vary strongly with pressure and isotopic masses. Pressure runs, up to 15 GPa, were performed at 16 K and 300 K. Whereas well-defined TO Raman phonons were observed at low temperature in the whole pressure range, at 300 K the TO phonons appear to hybridize strongly with the two-phonon background and lose their identity, especially in the (3–10)-GPa region. The intensity of the TO phonons, which nearly vanishes when measured with a red laser line, is shown to result from a destructive interference of the amplitudes of the band-edge resonance and that of a background of opposite sign. The analysis of these effects is aided by calculations of the densities of one- and two-phonon states performed with the adiabatic bond charge model of the lattice dynamics.
A novel ambient pressure microwave assisted technique is developed in which silver and indium-modified ZnS is synthesized. The as-prepared ZnS is characterized by x-ray diffraction, UV-vis spectroscopy, x-ray photoelectron spectroscopy and luminescence spectroscopy. This procedure produced crystalline materials with particle sizes below 10 nm. The synthesis technique leads to defects in the crystal which induce mid-energy levels in the band gap and lead to indoor light photocatalytic activity. Increasing the amount of silver causes a phase transition from cubic blende to hexagonal phase ZnS. In a comparative study, when the ZnS cubic blende is heated in a conventional chamber furnace, it is completely converted to ZnO at 600 °C. Both cubic blende and hexagonal ZnS show excellent photocatalytic activity under irradiation from a 60 W light bulb. These ZnS samples also show significantly higher photocatalytic activity than the commercially available TiO(2) (Evonik-Degussa P-25).
Compared with traditional filter paper, high-purity cellulose membrane prepared via green pathway was used to enhance detection performance for cadmium ions. In this work, a simple, rapid and highly sensitive cellulose membrane-based colorimetric sensor strip (CCSS) for efficient detection of trace Cd (II) in water has been designed. Cellulose membrane (CM) was prepared by a tape casting method. Victoria blue B (VBB) was used as an indicator and was bound in the CM matrix through intermolecular hydrogen bonds. The morphology, structure, and properties of CM and CCSS were characterized by SEM, FTIR and BET. The detection and anti-interference performance of CCSS for cadmium ions was investigated. In addition, the design and chromogenic reaction mechanism of CCSS were also studied. The results showed that CCSS was successfully prepared. The specific surface area, pore volume and pore size of CCSS were decreased after VBB loading. The color of the CCSS changed from yellow to blue-green after cadmium ions were added. The limit of detection (LOD) was as low as 0.01 mg L-1 with the naked eye, and the fast response time of strip for Cd (II) was 1 min . The CCSS was successfully applied to real water samples with strong anti-interference ability. KEYWORDS: Colorimetric sensor; Cellulose membrane; Victoria blue B; Detection; Cadmium ions; Intermolecular hydrogen bonds
In order to achieve the global goals related to renewable energy and responsible production, technologies that ensure the circular economy of metals and chemicals in recycling processes are a necessity. The recycling of spent Nd-Fe-B magnets typically results in rare earth elements (REEs) free wastewaters that have a high ferric ion concentration as well as oxalate groups and for which, there are only a few economically viable methods for disposal or reuse. The current research provides a new approach for the effective recovery of oxalic acid and the results suggest that during the initial oxalate groups separation stage, > 99% of oxalate ions can be precipitated as ferrous oxalate (FeC2O4·2H2O) by an ultrasound-assisted iron powder replacement method (Fe/Fe(III) = 2, tu/s = 5 min, T = 50 °C). Subsequently, almost all of the FeC2O4·2H2O was dissolved using 6 mol/L HCl (T = 65 °C, t = 5 min) and the dissolved oxalates were found to mainly exist in form of H2C2O4. Furthermore, over 80% of the oxalic acid was recovered via crystallization by cooling the oxalate containing HCl solution to 5 °C. After oxalic acid crystallization, the residual raffinate acid solution can then be recirculated back to the ferrous oxalate leaching stage, in order to decrease any oxalic acid losses. This treatment protocol for high iron REEs-free solution not only avoids the potential harm to the environment due to the wastewater but also significantly improves the circular economy of chemicals in the typical utilized in permanent magnet recycling processes.
Despite of useful applications of Ag, it is hazardous to health and environment and hence early detection is required. Crystal defects influencing optical property is less likely utilized for Ag detection using prevalent UV-Vis technique. Quantum dots (QDs) ZnS prepared by soft chemical route are exploited for the detection of Ag+ in aqueous solution for nM to mM concentrations. UV-Vis and photoluminescence (PL) measurements reveal quantum confinement effect and presence of defects in ZnS nanoparticles (NPs). Controlled synthesis of ZnS NPs allows appearance of defects related peak at 400–550 nm in UV-Vis spectra. A plausible mechanism is presented and elucidated by XRD and PL studies for chemical interaction between ZnS with Ag+. The interaction affects prominently the defects related absorption of ZnS NPs and allows single step Ag+ detection in aqueous medium. This absorption method is extended to other ions (Na+, K+, Mg+, Ca+, Ba+) including ‘S’ prone heavy and toxic ions like Pb, Hg, and Cd. Among them, Ag+ shows the best response with ZnS NPs. This demonstration using a portable and cost effective technique with no organic component opens up possibility for other inorganic materials.
Plasmonic nanoparticles offer promise in photoelectrochemistry by enhancing the rate and selectivity of reactions and in sensing by responding optically to local reactions. Optical electrochemical measurements at the single-particle level are necessary for understanding and eventually controlling the role of plasmons in such complex environments. Recently, researchers have developed techniques to optically measure electrochemical reactions at the surface of single nanoparticles and individual aggregates, allowing for the high-throughput screening necessary to resolve subpopulations of active nanoparticle catalysts and identify active sites on aggregate structures. This review highlights single-nanoparticle and nanoparticle aggregate electrochemical techniques and how they can be used to isolate and elucidate the role of surface plasmons in enhancing catalyst activity and sensing electrochemical processes at the nanoscale.
Nanoparticles exist far from the equilibrium state due to their high surface energy. Nanoparticles are therefore extremely unstable and easily change themselves or react with active substances to reach a relatively stable state in some cases. This causes desired changes or undesired changes to nanoparticles and thus makes them exhibit a high reactivity and a poor stability. Such dual nature (poor stability and high reactivity) of nanoparticles may result in both negative and positive effects for nanoparticle processing. However, the existing studies mainly focus on the high reactivity of nanoparticles, whereas their poor stability has been neglected or considered inconsequential. In fact, in some cases the unstable process, which is derived from the poor stability of nanoparticles, offers an opportunity to design and fabricate unique nanomaterials, such as by chemically transforming the “captured” intermediate nanostructures during a changing process, assembling destabilized nanoparticles into larger ordered assemblies, or shrinking/processing pristine materials into the desired size or shape via selective etching. In this review, we aim to present the stability and reactivity of nanoparticles on three levels: the foundation, concrete manifestations, and applications. We start with a brief introduction of dangling bonds and the surface chemistry of nanoparticles. Then, concrete manifestations of the poor stability and high reactivity of nanoparticles are presented from four perspectives: dispersion stability, thermal stability, structural stability, and chemical stability/reactivity. Next, we discuss some issues regarding the stability and reactivity of nanomaterials during applications. Finally, conclusions and perspectives on this field are presented.
Wearable electronics is expected to be one of the most active research areas in the next decade, therefore, nanomaterials possessing high carrier mobility, optical transparency, mechanical robustness and flexibility, light-weight, and environmental stability will be in immense demand. Graphene is one of the nanomaterials that fulfill all these requirements, along with other inherently unique properties and convenience to fabricate into different morphological nanostructures, from atomically thin single layers to nanoribbons. Graphene-based materials have also been investigated in sensor technologies, from chemical sensing to detection of cancer biomarkers. The progress of graphene-based flexible gas and chemical sensors in terms of material preparation, sensor fabrication, and their performance are reviewed here. The article provides a brief introduction to graphene-based materials and their potential applications in flexible and stretchable wearable electronic devices. The role of graphene in fabricating flexible gas sensors for the detection of various hazardous gases, including nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), sulfur dioxide (SO2), and humidity in wearable technology, is discussed. In addition, applications of graphene-based materials are also summarized in detecting toxic heavy metal ions (Cd, Hg, Pb, Cr, Fe, Ni, Co, Cu, Ag), and volatile organic compounds (VOCs) including nitrobenzene, toluene, acetone, formaldehyde, amines, phenols, bisphenol A (BPA), explosives, chemical warfare agents, and environmental pollutants. The sensitivity, selectivity and strategies for excluding interferents are also discussed for graphene-based gas and chemical sensors. The challenges for developing future generation of flexible and stretchable sensors for wearable technology that would be usable for the Internet of Things (IoT) are also highlighted.
Aluminum is a health hazard element, found abundantly in the environment. Although many methods have been reported for the efficient detection of aluminum, an easy and accessible sensor for fast detection of aqueous aluminum has not been devised to date. In this approach, we have synthesized indole-2-carboxylic acid capped silver nanoparticles (I2CA-AgNPs) using the one-pot method and used them as label-free nanosensors for the detection of Al3+ in the presence of interfering metal ions. I2CA-AgNPs were synthesized by two methods at different temperatures. AgNPs synthesized by heating method were further used as detection probe as they showed a strong and narrow surface plasmon resonance (SPR) peak in the visible region. The sensitivity of the detection probe has been optimized by variations in size and distribution of nanoparticles. Synthesized AgNPs were characterized by UV-Vis spectroscopy, HRTEM, FT-IR, zeta potential and DLS analysis. Based on these results, I2CA-AgNPs could be used as a colorimetric sensor to selectively detect the presence of Al3+. Further, Results are confirmed by theoretical calculations of binding energy by DFT. Moreover, the nanosensor can also be applied to trace aluminum contamination in different types of water samples. The lower detection limit of the proposed method is 0.01 ppm (S/N = 3) which falls in the permissible limit set by USEPA i.e. 50 ppm.
A facile and green synthetic route is developed to prepare water soluble, green-fluorescent Pt, Au, Ag and Cu quantum clusters (QCs), employing innoxious l-histidine as a capping agent. These metal QCs give out emissions at 455-495 nm, with maximum excitation wavelengths ranging between 350 and 401 nm. Interestingly, these histidine-stabilized metal quantum clusters also possess non-linear optical properties like two-photon luminescence, which is detected when they are exposed to a femtosecond laser at 812 nm. Luminescence quantum yields of Pt (2.93%), Au (13.10%), Ag (6.97%) and Cu (8.29%) clusters are found to be distinctly different, and lifetime measurement results suggest that the emissions of metal clusters (4.59-7.39 ns) stem from singlet transitions among different electron energy levels rather than metal-ligand electron transfer behaviors. The Pt, Au, Ag and Cu quantum clusters have average sizes of 1.3-1.9 nm, and are mainly composed of 11, 9, 4 and 7 metal atoms, respectively, according to the electrospray ionization mass spectrometry results. Moreover, the as-prepared metal clusters are sensitive to aqueous ferric ions, both as highly selective fluorescent and colorimetric probes in a low and wide concentration range, and are promising in many biological applications.
Development of novel composite materials with enhanced optical properties and modified surface morphology is highly significant in surface enhanced Raman spectroscopic (SERS) applications. Dielectric-plasmonic multilayer composites are found to serve this purpose due to the feasibility of tuning their plasmon resonances even to IR region, far away from electronic resonance of analyte molecules. In this work, we introduce a new composite material that can have enormous potential in sensing applications at trace level. Here we demonstrate surface enhanced Raman scattering activity of [email protected]/* */3O4@Ag composite structures using rhodamine 6G (Rh6G) dye molecule as the model analyte. The SERS substrate is prepared by coating these structures on borosilicate glass substrate. ZnS particles of size 300 nm coated successively with Fe3O4 (40 nm thick) and Ag (20 nm thick) nanoparticles are found to be capable of detecting even 10⁻¹¹ M concentration of Rh6G. Obtained results are compared with SERS activity of [email protected]/* */ particles which could detect only up to 10⁻⁸ M of Rh6G. It is observed that inclusion of Fe3O4 layer increases SERS enhancement by a factor of 10² compared to that of [email protected]/* */ SERS substrates fabricated out of [email protected]/* */3O4@Ag particles resulted in SERS enhancement factor (EF) of around 10⁹ which is large enough for single molecule detection. Theoretical investigations on SERS activity of these structures are carried out using finite difference time domain (FDTD) method. SERS EFs obtained using FDTD are found to be in good agreement with experimental results.
A bare platinum disk electrode without further decoration was directly used to determine oxalic acid (OA), showing good linear ranges of 0.57–104.01 μM and 104.01–228.75 μM with a low detection limit of 0.38 μM (S/N = 3). In contrast, platinum nanoparticles (PtNPs) dispersed on a glassy carbon electrode were successfully achieved by an one-step electrochemical deposition method, possessing relatively wider linear detection ranges of 1.14–342.80 μM and 342.80–548.92 μM for OA with a lower detection limit of 0.28 μM (S/N = 3). Both the proposed electrochemical sensors exhibit great reproducibility, stability and selectivity. In particular, they have been applied to the determination of OA in real spinach samples, showing excellent analytical performance.
In this study, a nanohybrid of gold nanoparticle, polypyrrole, and reduced graphene oxide (AuNP/PPy/rGO) was prepared by an in-situ chemical synthesis approach. The as-prepared nanohybrid has been applied for non-enzymatic electrochemical detection of oxalic acid (OA). The nanohybrid nanocomposite material (AuNP/PPy/rGO) was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and cyclic voltammetry (CV), and further employed as novel sensing material to quantify OA. Compared with PPy/rGO, the AuNP/PPy/rGO nanocomposite showed enhanced electrocatalytic activity towards OA oxidation. The oxidation current of OA is linear to its concentration in the range of 0.05 mM to 7mM with a lower detection limit of 0.02mM. The experimental results also showed that the fabricated sensor has good reproducibility (R.S.D=2.59% for 0.5mM, n=3), high sensitivity (91μA/mM), excellent stability and good anti-interference property against electroactive compounds and metal ions.
Conversion of cellulose into value-added chemicals and/or fuels has attracted worldwide attention due to the dwindling fossil fuel reserves and concerns over global warming. Herein, the conversion of microcrystalline cellulose into oxalic acid in homogeneous NaOH solution catalyzed by metal oxides under low oxygen pressure was reported. The effects of metal oxides, reaction temperature, reaction time, and oxygen pressure on the yields of the major products were studied. The results showed that a high yield of organic acids, mainly including oxalic acid, formic acid, glycolic acid, lactic acid, and acetic acid, could be obtained. Catalytic amounts of CuO could effectively improve the yield of oxalic acid. The yield of the oxalic acid could be as high as 41.5% with catalytic amount of CuO at oxygen pressure of 0.3 MPa and 200 °C for 2 h. A tentative reaction pathway for the selective oxidation of cellulose into small molecular organic acids in aqueous NaOH solution was investigated and proposed.
In this paper, we developed an electrochemical sensor for the detection of oxalic acid (OA). The electrochemical sensor was prepared by hydrothermal synthesis of three dimensional (3D) graphene aerogel (GA). The obtained sensor was characterized by a series of techniques. It was found that the GA modified GCE displays excellent catalytic property toward the oxidation of OA, which make it became an enzymeless sensor with high selectivity, good reproducibility and stability. The sensor shows a linear relation towards OA detection in the concentration of 4 to 100 μM with a low detection limit of 0.8 μM. Moreover, the proposed sensor was used for OA detection in tomato and onion samples.
In this paper, a new electrochemical oxalic acid (OA) sensor based on graphene (GR)-modified carbon ionic liquid electrode (CILE) was proposed. The GR nanosheets were deposited on the surface of CILE by electroreduction with graphene oxide as precursor and electrocatalytic oxidation of OA on GR/CILE was further investigated. As compared with that of bare CILE, the oxidation peak current of OA on GR/CILE were greatly improved with the decrease of the oxidation potential. Electrochemical parameters of the electrooxidation of OA were calculated. Under the selected conditions, the oxidation peak currents increased with OA concentration in the range from 8.0 μM to 6.0 mM with the detection limit as 0.48 μM (3σ). The proposed method exhibited higher sensitivity and wider linear range, which was applied to determination of OA concentration in spinach samples with satisfactory results.
A novel kinetic chemiluminescent method has been proposed for the simultaneous determination of oxalic acid (OA) and citric acid (CA). The method is based on the catalytic effect of OA and CA in the chemiluminescence (CL) reaction of tris(1,10-phen)ruthenium(II) with Ce(IV). In the batch mode, OA gives a broad peak with the highest CL intensity at 0.7 second, whereas the maximum CL intensity of the CA appears at about 4.7 seconds after injection of Ce(IV) solution. Based on the differential rate of the CL reaction corresponding to CA and OA and different effect of Ce(IV) concentration on the CL intensity of these substances, a three dimension data and multi-way partial least squares (N-PLS) regression method was developed for the simultaneous determination of CA and OA. After selecting the best operating parameters, calibration graphs were obtained over the concentration ranges 4.0×10-8-2×10-5 mol L-1 and 2.0×10-7-2.0×10-4 mol L-1for OA and CA, respectively. The limits of detections were 2.0×10-8 mol L-1 for OA and 1.0×10-7 mol L-1 for CA. Relative standard deviation (RSD) of the method for 11 times simultaneous determination of 1.6×10-6 mol L-1 of OA and 3.2×10-6 mol L-1 of CA were 7.5% and 2.9%, respectively. The proposed method was successfully applied to the determination of the mixtures in synthetic sample, stain remover and anti-varroa mite formulations.
The acidity developed by elemental sulphur when mixed with neutral water has been studied by measurements of the variaiion of pH with changes in the ratio of the solid sulphur to water and the effect of the presenece of metallic iron. The results obtained have been shown to extend the data reported at high temperature and high pressuee (145°c to 288°c and 100 MN.m−2, respeciively) to ambient temperatures. Complete agreement was found between the values of the concentration of H2S and H2SO4 calculated ror low temperature and atmospheric pressure and the values reported from chemical analysis. The hydrolysis of sulphur in water consists of the disproportionation of the octa-atomic sulphur (S8) into oxidised and reduced compounds in the ratio H2S/H2SO4 = 3/1. The activation energy for the hydrolysis of sulphur in water over a wide range of temperature (15° to 288°c) is in the range, 40–52 kJ. mol−1. Elemental sulphur in the presenee of water acts as a ‘hydrogen ion carrier’, with the tendency to produce hydrogen ions concentrated at the surface of solid particles. A study of the corrosion of iron by sulphur–water mixtures has shown that an induction stage exists where pH increases as corrosion occurs with an increase in the disproportionation of elemental sulphur, stimulated by the removal of HS ions reacting with the ions produced by the dissolving surface.
Colloidal semiconductor nanocrystals or quantum dots (QDs) have been facilitating the development of sensitive fluorescence sensors over the past decade, due to their unique photophysical properties, versatile surface chemistry and ligand binding ability, and the possibility of the encapsulation in different materials or attachment to different functional materials, while retaining their native luminescence property. The optical metal ion chemosensors with high sensitivity and selectivity have been developed due to the importance of the metal ions' fundamental roles, possessed in a wide range of biological processes and the aquatic environment. This review addresses the different sensing strategies with chemically modified QD hybrid structures for the sensing of metal ions in aqueous solution or an in vivo environment, and discusses the photophysical mechanisms in the different sensor systems while comparing their detecting/sensing selectivity. The perspectives for the future potential developments in QD based optical sensing for metal ions are discussed.
An ionic liquid functionalized graphene film was prepared and PdAu nanoparticles (NPs) were electrodeposited on it. The PdAu NPs were characterized by various methods and they showed the features of alloys. In 0.2 M H2SO4 solution, oxalic acid (OA) exhibited a sensitive anodic peak at the resulting electrode at about 1.1 V (vs. SCE), and the peak current was linear to OA concentration in the range of 5–100 µM with a sensitivity of 45.5 µA/mM. The detection limit was 2.7 µM (S/N=3). The electrode was successfully applied to the determination of OA in real sample.
Luminescent carbon-based nanoparticles, addressed as carbon dots (CDs), were synthesized at relatively low temperature from lactose following an easy and inexpensive procedure. Modification of their surface was done by functionalization with mercaptosuccinic acid (MSA) (CDs-MSA). Transmission electron microscopy images showed regular spherical nanoparticles of 5 nm in diameter. Raw and functionalized (CDs-MSA) were highly fluorescent at 448 and 472 nm, with relative high quantum yield (Φ= 0.21 and 0.46 respectively). At maximum fluorescence of CDs-MSA the intensity was quenched by addition of Ag+ ions by a static mechanism with Stern-Volmer constant of 3.7×103 M-1. The analysis of the emission spectra showed that the CD-MSA complex was stable after this process. The quenching profiles showed that only 44 % of the CD-MSA fluorophores are accessible to Ag+. The main figures of merit were a detection and quantification limits of 385.8 nM and 1.2 μM respectively, and the precision as relative standard deviation was 1.76 %. No interferences were observed when other metal ions were present indicating a high selectivity of Ag+ detection. The results showed that CDs-MSA can be used in efficient quantification of free Ag+ in silver nanoparticles dissolution.
We report Raman scattering results of wurtzite ZnS nanowires, nanocombs, and nanobelts. The Raman spectrum obtained from ZnS nanowires exhibits first‐order phonon modes at 272, 284, and 350 cm−1, corresponding to A1/E1 transverse optical, E2 transverse optical, and A1/E1 longitudinal optical phonons, respectively. Several multiphonon modes are also observed. The longitudinal optical phonon mode varies in wavenumber for nanocombs and nanobelts, indicating that the residual strain varies during the morphological change from ZnS nanowires to nanocombs and ultimately to nanobelts. Interestingly, a surface optical (SO) phonon mode varies in wavenumber depending on the shape and surface roughness of the ZnS nanostructures. The surface modulation wavelengths of the ZnS nanowires, nanocombs, and nanobelts are estimated using the SO phonon dispersion relations and the observed SO phonon wavenumbers. Copyright © 2012 John Wiley & Sons, Ltd.
The effects of S-vacancy and Zn-vacancy on the geometric and electronic structures of zinc blende ZnS are investigated by the first-principles calculation of the plane wave ultrasoft pseudopotential method based on the density functional theory. The results demonstrate that both S-vacancy and Zn-vacancy decrease the cell volume and induce slight deformation of the perfect ZnS. Furthermore, this change of geometric structure caused by Zn-vacancy is more obvious than the one due to the S-vacancy. The formation energy of S-vacancy is higher than that of Zn-vacancy, indicating that Zn-vacancy is easier to form than S-vacancy in ZnS crystal. Electronic structure analysis shows that Zn-vacancy increases the band-gap of ZnS from 2.03 eV to 2.15 eV, while the S-vacancy has almost no effect on the band-gap of ZnS. Bond population analysis shows that Zn-vacancy increases covalence character of the Zn–S bonds around Zn-vacancy, while S-vacancy shows a relatively weak effect on the covalence character of Zn–S bonds.
Due to their unique optical properties, quantum dots (QDs) are rapidly revolutionizing many areas of medicine and biology. Despite the remarkable speed of development of nanoscience, relatively little is known about the interaction of nanoscale objects with organism. In this work, interaction of CdTe QDs coated with mercaptopropanoic acid (MPA), L-cysteine (L-cys), and glutathione (GSH) with bovine serum albumin (BSA) was investigated. Fluorescence (FL), UV–vis absorption, and circular dichroism (CD) spectra methods were used. The Stern-Volmer quenching constant (Ksv) at different temperatures, corresponding thermodynamic parameters (ΔH, ΔG and ΔS), and information of the structural features of BSA were gained. We found that QDs can effectively quench the FL of BSA in a ligand-dependent manner, electrostatic interactions play a major role in the binding reaction, and the nature of quenching is static, resulting in forming QDs-BSA complexes. The CD spectra showed that the secondary and tertiary structure of BSA was changed. This study contributes to a better understanding of the ligand effects on QDs-proteins interactions, which is a critical issue for the applications in vivo.
The electrochemical oxidation of oxalic acid (OA) has been studied, in acidic media, at Ti/PbO2, highly boron-doped diamond (BDD), Pt, Au and Ti/IrO2–Ta2O5 electrodes, by both cyclic voltammetry and bulk electrolysis. The anodic oxidation of OA has clearly shown that the electrode material is an important parameter when optimizing such processes, since the mechanism and the products of several anodic reactions are known to depend on the anode material. OA was oxidized at several substrates to CO2 with different results; however, higher current efficiencies were obtained at Ti/PbO2, Pt and BDD. At Ti/PbO2, the carboxylic groups are expected to strongly interact with the Pb(IV) sites and the hydroxyl radical formed on/at the electrode surface. In some cases, complex interactions exist between the organic substrate and the electrode surface, as confirmed by the oxidative behavior of OA at the Pt electrode.
The development of a new amperometric biosensor for oxalate utilising two enzymes, oxalate oxidase (OXO) and horseradish peroxidase (HRP), incorporated into carbon paste electrode modified with silica gel coated with titanium oxide containing toluidine blue is described. OXO has been immobilised on silica gel modified with titanium oxide surface using glutaraldehyde for crosslinking. HRP has been immobilised with covalent binding with carbodiimide on graphite powder. The biosensor showed a good performance with a linear response range between 0.1 and 2.0mmoll−1 of oxalate, fit by the equation i=0.33(±0.04)+2.29(±0.04) [oxalate], where i is the current in μA and [oxalate] is the oxalate concentration in mmoll−1 with a correlation coefficient of 0.998 for n=20. The biosensor could be used for 80 determinations when stored in a succinate buffer at pH 3.8 in a refrigerator. The response time was about 0.5s. The detection limit, considering three times the noise, was 0.09mmoll−1 for oxalate. The time for oxalate determination in spinach samples decreased by 3 days when this biosensor was used, compared to the AOAC method.
The catalytic ozonation of oxalic acid in a batch reactor using TiO 2, MnO2/TiO2 and Rh/TiO2 as catalysts was studied. The presence of the catalyst significantly improves the ozonation rate in comparison with the noncatalytic reaction. The adsorption and the extent of degradation of oxalic acid were found to be dependent on the solution's pH. Higher degradation rates were found for catalytic systems at pH 2.5, where the oxalic acid concentration in the water phase was almost completely removed. The contribution of the MnO2/TiO2 and Rh/TiO2 catalysts as well the TiO2 support is discussed. The highest mineralization, expressed as CO2 evolution, was reached with the MnO2/TiO2 catalyst at pH 2.5.
We present a detailed study of the first- and second-order Raman effect in cubic ZnS using both 4880 and 5145 Å excitation. Our primary interest is to determine to what extent information on lattice dynamics can be extracted from Raman studies in a case where the crystal structure is relatively simple. Aside from interpreting the observed spectra and determining the energies of the phonon branches at the Brillouin-zone center and boundary, the study emphasizes two things. First, we examine experimentally the relation between first-order Raman intensities and the linear electro-optic effect. We find that the linear electro-optic constant derived from the absolute Raman intensities of the longitudinal- (LO) and transverse- (TO) optic modes agrees quite well with the constant obtained from direct measurement. This close agreement is particularly significant in the zinc-blende structure, since only one electro-optic constant and two optical modes are involved in the comparison. Also, it provides experimental evidence that the macroscopic, and not the local, electric field caused by the polar phonons should be used in calculations involving semiconducting crystals. Second, emphasis was also placed on comparing the observed selection rules or polarization properties of the second-order Raman effect with that predicted at the two most important or highest-symmetry critical points (X and L) on the Brillouin-zone boundary. The agreement between observed and calculated selection rules is quite good, although in some cases, certain polarization characteristics which are allowed by symmetry are not detected. Also, some evidence of two-phonon scattering from other points in the Brillouin zone is found. The polarization properties of single-crystal Raman spectra are more conveniently discussed in terms of the irreducible representations of the polarizability, rather than depolarized spectra or depolarization ratios which apply more directly to liquid or polycrystalline samples. The observed and calculated selection rules for second-order Raman scattering are compared in detail, using these polarizability representations. The LO and TO phonon energies are 271 and 352 cm-1 at the zone center and 306 and 333 cm-1 at the zone boundary, and the TA and LA energies are 88 and 110 cm-1 at the boundary.
Raman spectra of wurtzite- and zinc-blende-type ZnS single crystals were excited by a He-Ne laser (6328 Å) and an argon-ion laser (4880 Å and 5145 Å). All the Raman-active long-wavelength phonon frequencies were determined. These are (i) for the cubic modification, TO=276 cm-1 and LO=351 cm-1; and (ii) for the hexagonal modification, E2=72 cm-1, E2=286 cm-1, A1(TO)=E1(TO)=273 cm-1, and A1(LO)=E1(LO)=351 cm-1. The lowest-frequency E2 mode of the mixed crystal system CdxZn1-xS was studied as a function of x, and was found to vary monotonically. The intensity ratio of the LO to the TO band seems to be dependent on the wavelength of the exciting radiation.
An enzyme-free oxalic acid (OA) electrochemical sensor was assembled using a platinum nanoparticle-loaded graphene nanosheets (PtNPGNs)-modified electrode. The PtNPGNs, with a high yield of PtNPs dispersed on the graphene nanosheets, were successfully achieved by a green, rapid, one-step and template-free method. The resulting PtNPGNs were characterized by transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and an X-ray diffraction technique. Electrochemical oxidation of OA on the PtNPGNs-modified electrode was investigated by cyclic voltammetry and differential pulse voltammetry methods. Based on the results, the modified electrode exhibited high electrochemical activity with well-defined peaks of OA oxidation and a notably decreased overpotential compared to the bare or even the GNs-modified electrode. Under optimized conditions, a good linear response was observed for the concentration of OA and its current response was in the range of 0.1-15 mM and 15-50 mM with a detection limit (S/N = 3) of 10 μM. Furthermore, the electrochemical sensor presented good characteristics in terms of stability and reproducibility, promising the applicability of the sensor in practical analysis.
The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.
ZnS nanobelts with a pure wurtzite phase have been synthesized by a thermal evaporation method with the assistance of H2S in an Ar atmosphere. Photoluminescence band centered at about 535 nm has been observed under excitation in the range of 250–480 nm with decay rate as short as 860 ps. The origin of this intense photoluminescence is related to elemental sulfur species on the surface of the ZnS nanobelts. This assignment is substantiated by structural analysis by high-resolution electron microscopy, x-ray photoelectron spectroscopy, and photoluminescence and excitation technique. ZnS nanobelts with intense surface photoluminescence could be used as effective green light emitters, humid sensors, and UV light detectors.
Zinc sulfide (ZnS) is one of the first semiconductors discovered. It has traditionally shown remarkable versatility and promise for novel fundamental properties and diverse applications. The nanoscale morphologies of ZnS have been proven to be one of the richest among all inorganic semiconductors. In this article, we provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures. We begin with a historical background of ZnS, description of its structure, chemical and electronic properties, and its unique advantages in specific potential applications. This is followed by in-detail discussions on the recent progress in the synthesis, analysis of novel properties and potential applications, with the focus on the critical experiments determining the electrical, chemical and physical parameters of the nanostructures, and the interplay between synthetic conditions and nanoscale morphologies. Finally, we highlight the recent achievements regarding the improvement of ZnS novel properties and finding prospective applications, such as field emitters, field effect transistors (FETs), p-type conductors, catalyzators, UV-light sensors, chemical sensors (including gas sensors), biosensors, and nanogenerators. Overall this review presents a systematic investigation of the ‘synthesis-property-application’ triangle for the diverse ZnS nanostructures.