Harmful Organic Pollutants Research Articles

A high-performance NiMoO4/g-C3N4 direct Z-scheme heterojunction photocatalyst for the degradation of organic pollutants

Photocatalytic degradation of harmful organic pollutants in water has been considered an important research subject due to its efficient and cost–effective handling of toxic substances for ecosystems protection. We report a direct Z–scheme heterojunction photocatalyst made up of NiMoO4/g–C3N4 (NMOCN) nanocomposite for degrading the antibiotic, i.e., ciprofloxacin (CIP) and the organic dye, i.e., malachite green (MG). The nanocomposites were systematically prepared, and their structural, morphological, optical, and photoelectrochemical properties were analyzed. XRD analysis verified that NiMoO4 had a monoclinic crystal structure. The FESEM and HRTEM images showed that NMOCN composites were comprised of NiMoO4 nanorods coupled with g-C3N4 nanosheets. UV−VIS absorbance spectral analyses showed that NMOCN composites had a narrow band gap with good visible light absorption properties. Mott–Schottky and EIS measurements revealed that NMOCN composites had an optimum band structure and low charge transfer resistance for heterojunction formation. Increasing the relative mass content of g–C3N4 in NMOCN composites improved the photocatalytic degradation efficiency. NMOCN–30 (30 wt.% of g–C3N4) composite provided a maximum degradation efficiency, i.e., 90.82% for CIP (in 75 min) and 98.84% for MG (in 120 min), while showing excellent stability against CIP and MG up to six consecutive cycles. In addition, the EPR measurement and trap test results proved that all ·OH, ·O2–, and h+ participated in photodegradation activity. Thus, the presented nanocomposite photocatalysts with a Z–scheme heterojunction can help to build up a viable strategy for water pollution treatment with enhanced photocatalytic degradation capabilities.

Controllable synthesis of Ce-doped ZnO: TiO2 nanospheres for photocatalytic degradation of MB dye and levofloxacin under sunlight light irradiation

Wastewater from the textiles and pharmaceutical industries contains harmful inorganic and organic pollutants, which is not only harmful for aquatic life but also mutagenic to human. To minimize these problems, photocatalytic degradation is the one of the most promising remediation method. In the present work Ce doped ZnO:TiO2 nanocomposite powder samples, taking concentration as 0, 0.5, 1, and 1.5 at% coded as CZT1, CZT2, CZT3 and CZT4, respectively were synthesized. As prepared powder samples were characterized by various techniques including XRD, FE-SEM, UV–Vis Spectrophotometer and Photoluminescence. The X-ray diffraction pattern examined, all samples contains polycrystalline nature and their crystallite size was, from 5.06 nm to 2.3 nm as the doping concentration of Ce was increased. Field-emission scanning electron microscopy (FE-SEM) demonstrates the surface morphology of powder samples and determined the nanosphere like morphology. The bandgap of the samples varying from 3.36 eV to 2.62 eV, whereas the photoluminescence spectra (PL) of the sample show the visible emission at 475 nm. The CZT nanocomposite powder samples were characterized for the photocatalytic degradation of the Levofloxacin and MB dye. The degradation efficiency of the samples for was obtained for MB and levofloxacin i.e. 98% and 97.5% respectively.

Hydrothermal Synthesis of Heterostructured g-C3N4/Ag-TiO2 Nanocomposites for Enhanced Photocatalytic Degradation of Organic Pollutants.

In this study, heterostructured g-C3N4/Ag-TiO2 nanocomposites were successfully fabricated using an easily accessible hydrothermal route. Various analytical tools were employed to investigate the surface morphology, crystal structure, specific surface area, and optical properties of as-synthesized samples. XRD and TEM characterization results provided evidence of the successful fabrication of the ternary g-C3N4/Ag-TiO2 heterostructured nanocomposite. The heterostructured g-C3N4/Ag-TiO2 nanocomposite exhibited the best degradation efficiency of 98.04% against rhodamine B (RhB) within 180 min under visible LED light irradiation. The g-C3N4/Ag-TiO2 nanocomposite exhibited an apparent reaction rate constant 13.16, 4.7, and 1.33 times higher than that of TiO2, Ag-TiO2, and g-C3N4, respectively. The g-C3N4/Ag-TiO2 ternary composite demonstrated higher photocatalytic activity than pristine TiO2 and binary Ag-TiO2 photocatalysts for the degradation of RhB under visible LED light irradiation. The improved photocatalytic performance of the g-C3N4/Ag-TiO2 nanocomposite can be attributed to the formation of an excellent heterostructure between TiO2 and g-C3N4 as well as the incorporation of Ag nanoparticles, which promoted efficient charge carrier separation and transfer and suppressed the rate of recombination. Therefore, this study presents the development of heterostructured g-C3N4/Ag-TiO2 nanocomposites that exhibit excellent photocatalytic performance for the efficient degradation of harmful organic pollutants in wastewater, making them promising candidates for environmental remediation.

Synergistic combination of BiFeO3 nanorods and CeVO4 nanoparticles for enhanced visible light driven photocatalytic activity

Eliminating harmful organic pollutants from contaminated water remains an urgent problem to be solved. Taking Rhodamine B (RhB) as a representative organic water pollutant we sought to design a facile and scalable synthesis of a BiFeO3/CeVO4 (BFO/CVO) nanocomposite catalyst for the degradation of organic pollutant under visible light. BFO nanorods and CVO nanoparticles were fabricated using single-step hydrothermal routes and the resulting materials could be easily combined using a simple wet-chemical precipitation method. From the morphological studies, pure BiFeO3 and CeVO4 revealed the 1D-nanorod and 0D-nanoparticles, respectively. For the BFO/CVO composite, 0D-nanoparticles were well attached on the 1D-nanorods of BiFeO3. Also, the 10 % BFO/CVO composite provided efficient photodegradation efficiency (92 %) of RhB with 0.0225 min−1 rate constant. Furthermore, the obtained photocatalyst had a low band gap energy value (2.01 eV) and photoluminescence intensity when compared to pure BFO and CVO under visible light illumination. The radical scavenging experiments proposed that the •OH acted a substantial role in the RhB decomposition pathway. The optimized BFO/CVO composite photocatalyst exhibits superior recyclability and photostability. The superior photocatalytic action of the 10 % BFO/CVO composite could be explained by the development of a heterojunction among BFO and CVO where electrons can migrate at the BFO/CVO interface. These results imply that BiFeO3/CeVO4 composites are suitable photocatalysts for the elimination of organic toxins from water.

Enhanced photocatalytic degradation of organic dye by CeO2/CNT/GO hybrid nanocomposites under UV light for wastewater treatment.

Development of nanocomposites as efficient photocatalysts for the removal of hazardous organic pollutants is always in dire demand due to increase in water pollution. In this article, a facile sol-gel method has been used to synthesize cerium oxide (CeO2) nanoparticles followed by their decoration over multi-walled carbon nanotubes (CNTs) and graphene oxide (GO) to construct binary as well ternary hybrid nanocomposites using ultrasonic treatment. The oxygen vacancy defects have been depicted using X-ray photoelectron spectroscopy (XPS) that may result into improved photocatalytic efficiency. The ternary hybrid nanocomposites (CeO2/CNT/GO) showed excellent photocatalytic efficiency towards degradation of rose bengal (RB) dye up to 96.9% in 50 min. CNTs and GO provide the interfacial charge transfer which inhibits the electron-hole pair recombination. The results obtained here indicate that these composites can be effectively utilized as promising materials for the degradation of harmful organic pollutants for wastewater treatment.

Preparation of visible light-WO3/g-C3N4/PANI photocatalyst onto glass and their photocatalytic properties

Wastewater from palm oil industry mostly contains hazardous effluent like palm oil mill effluent (POME) and photocatalytic technology is one of the most effective ways for the degradation of harmful organic pollutants. Nevertheless, the effects of suspended photocatalysts obviously would dwindle the photocatalytic performances. The immobilization of photocatalyst as a newest innovation has received significant attention due to its great potential in terms of recycling, economic, physical–chemical properties, and technological aspects. This paper reports the synthesis of novel WO3/g-C3N4/PANI glass as a retrievable visible-light photocatalyst by simple soft-templating and calcination followed by spin coating with different speed and duration coating. The functional group of O-W-O stretching vibration, hydrophilicity of the immobilized WO3/g-C3N4/PANI glass indicated the presence of WO3/g-C3N4/PANI onto glass was succesfully. The optimum parameters obtained were at a speed of 30 s and duration spinning of 1000 rpm due to the presence of more active sites. In particular, immobilized WO3/g-C3N4/PANI glass showed a good photocatalytic activity in term of decolorization and degradation studies about 25 % and 53 %, respectively, after 7 h under visible light irradiation and energy storage scheme. The results signify possible applications of immobilized WO3/g-C3N4/PANI glass in visible-light-driven and energy-storage-mechanism for a cost-effective treatment of wastewater.

Identification and Risk Assessment of Priority Control Organic Pollutants in Groundwater in the Junggar Basin in Xinjiang, P.R. China.

The Junggar Basin in Xinjiang is located in the hinterland of Eurasia, where the groundwater is a significant resource and has important ecological functions. The introduction of harmful organic pollutants into groundwater from increasing human activities and rapid socioeconomic development may lead to groundwater pollution at various levels. Therefore, to develop an effective regulatory framework, establishing a list of priority control organic pollutants (PCOPs) is in urgent need. In this study, a method of ranking the priority of pollutants based on their prevalence (Pv), occurrence (O) and persistent bioaccumulative toxicity (PBT) has been developed. PvOPBT in the environment was applied in the screening of PCOPs among 34 organic pollutants and the risk assessment of screened PCOPs in groundwater in the Junggar Basin. The results show that the PCOPs in groundwater were benzo[a]pyrene, 1,2-dichloroethane, trichloromethane and DDT. Among the pollutants, benzo[a]pyrene, 1,2-dichloroethane and DDT showed high potential ecological risk, whilst trichloromethane represented low potential ecological risk. With the exception of benzo[a]pyrene, which had high potential health risks, the other screened PCOPs had low potential health risks. Unlike the scatter distribution of groundwater benzo[a]pyrene, the 1,2-dichloroethane and trichloromethane in groundwater were mainly concentrated in the central part of the southern margin and the northern margin of the Junggar Basin, while the DDT in groundwater was only distributed in Jinghe County (in the southwest) and Beitun City (in the north). Industrial and agricultural activities were the main controlling factors that affected the distribution of PCOPs.

Research Progress in the Synthesis of Carbon Dots and Their Application in Food Analysis.

Food safety is connected to public health, making it crucial to protecting people's health. Food analysis and detection can assure food quality and effectively reduce the entry of harmful foods into the market. Carbon dots (CDs) are an excellent choice for food analysis and detection attributable to their advantages of good optical properties, water solubility, high chemical stability, easy functionalization, excellent bleaching resistance, low toxicity, and good biocompatibility. This paper focuses on the optical properties, synthesis methods, and applications of CDs in food analysis and detection, including the recent advances in food nutritional composition analysis and food quality detection, such as food additives, heavy metal ions, foodborne pathogens, harmful organic pollutants, and pH value. Moreover, this review also discusses the potentially toxic effects, current challenges, and prospects of CDs in basic research and applications. We hope that this review can provide valuable information to lay a foundation for subsequent research on CDs and promote the exploration of CDs-based sensing for future food detection.

Improved catalytic efficiency by N-doped TiO2 via sol gel under microwave irradiation: Dual applications in degradation of dye and microbes

The present research is to develop a facile and a fast microwave irradiation method to synthesise uniform and well-defined nitrogen-doped TiO2 nanocatalysts through the microwave-assisted sol-gel method. Advanced spectroscopic and analytical techniques are to be used to investigate the characteristics of the prepared catalyst samples. The synthesised nanocatalyst's XRD analysis shows lattice fringes for anatase phases. The XPS reveals the electronic state and composition of the dopant, which is almost consistent with the practically added concentration of dopant. The spectral shift (red shift) to the visible light region was demonstrated by the UV-visible diffuse reflectance spectroscopy analysis. The results demonstrated that NT3M4 has a reduced band gap of 2.56 ​eV. The HRTEM images of the NT3M4 analysis illustrate nanoparticles of spherical shape with a particle size of 6.3 ​nm. The surface properties and elemental composition were studied by SEM analysis, which depicts the irregular and rough morphology of the nanocatalysts. According to the Brunauer-Emmett-Teller (BET) results, NT3M4has a large surface area of 103 m2/g1. Type IV isotherms indicate the presence of the mesoporous structure in the nitrogen adsorption-desorption isotherm. The synthesised nanocatalyst NT3M4 demonstrated the best photocatalytic ability under visible light, which enhanced the rate of degradation of indigo carmine dye within 70 ​min. NT3M4 also exhibits antibacterial and antifungal activity. Further, this catalyst shows almost equal activity with standard chloramphenicol. Thus, the current study suggests microwave-assisted sol-gel methods for fabricating N-TiO2 nanocatalysts with the best photocatalytic performance for the degradation of harmful organic pollutants and pathogens in the presence of visible light irradiation.

Hydrothermal Synthesis of Cadmium Sulfide Photocatalyst for Detoxification of Azo Dyes and Ofloxacin Antibiotic in Wastewater.

The complete detoxification of harmful dyes and antibiotics from aqueous solution is essential for environmental remediation. The present work focuses on a facile hydrothermal synthesis of a cadmium sulfide (CdS) photocatalyst using thioacetamide as a sulfur source. The synthesized CdS showed a hexagonal phase with an energy gap of 2.27 eV, suggesting the promising visible-light-responsive semiconducting photocatalyst. The photoactivity of the prepared CdS was investigated by evaluating the degradation of the Reactive red 141 (RR141) dye, Congo red (CR) dye, and ofloxacin (OFL) antibiotic. After only 180 min of solar light illumination, a high performance of 98%, 97%, and 87% toward degradation of RR141, CR, and OFL was obtained. The photodegradation of the pollutants agrees well with the first-order kinetic model. The rate constant of 0.055 min-1, 0.040 min-1, and 0.026 min-1, respectively, was reported toward degradation of RR141, CR, and OFL. Photogenerated holes and hydroxyl radicals play a vital role in removing toxic organic contaminants. The chemical stability of the prepared CdS was also confirmed. The synthesized CdS photocatalyst still maintains high photocatalytic performance even after five consecutive cycles of use, indicating its excellent cycling ability. The present research shows a facile route to fabricate a CdS photocatalyst to completely detoxify harmful organic pollutants, including dyes and antibiotics, in the environment.

Synergic effect of Type II ZnO/BiVO4 magnetic heterostructures for visible light‐driven degradation of bisphenol A and methyl violet

Construction of an effective heterojunction for unimpeded flow of photogenerated charges and their prolonged separation is imperative for environmental photocatalysis. Herein, we have designed an efficient magnetic ZnO/BiVO4 type‐II heterostructure, which was employed for proficient degradation of persistent methyl violet dye with an efficiency of 97.6% in 90 min and a hazardous organic pollutant, namely, bisphenol A. UV‐DRS and photoluminescence studies demonstrated that the fabricated nanocomposite exhibited effective light absorption and prolonged charge separation, thereby resulting in high photocatalytic efficacy under visible light irradiation. The efficacy of developed magnetic ZnO/BiVO4 was also compared with pristine BiVO4 and undoped magnetic ZnO, which indicated that the constructed heterostructure displayed approximately threefold and sixfold activity in contrast with bare BiVO4 and undoped magnetic ZnO nanoparticles, respectively. Radical trapping studies, ESR analysis along with GC‐MS analysis were conducted to elucidate the mechanistic pathway during the photodegradation process. This work provides a rational technical approach and research ideas for photocatalytic degradation of harmful organic pollutants in an environment‐friendly manner by employing energy‐efficient LEDs. Besides, good recyclability of catalyst makes it a promising candidate for large‐scale applications.

Enriched surface oxygen vacancies of Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction with boosted visible-light photocatalytic degradation for levofloxacin: Performance, degradation pathway and mechanism insight

Exploring effective approach to promote more comprehensive charge transfer and efficient spatial charge separation is considered to be a prospective strategy to reinforce photocatalytic degradation activity. Herein, the oxygen vacancy modified Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction photocatalyst was successfully fabricated via a facile solvothermal method. The chemical structure, morphology, and optical properties of the photocatalyst were characterized in detail. The optimized Bi2WO6/NH2-MIL-68(In) Z-scheme heterojunction displayed the maximum photocatalytic efficiency (84.3 %) for the degradation of levofloxacin (LEV), which was significantly higher than that of pure Bi2WO6 (45.1 %), oxygen vacancy modified Bi2WO6 (69.4 %), and NH2-MIL-68(In) (49.3 %). Importantly, the high-resolution mass spectrometry (HRMS), three-dimensional excitation-emission matrix (3D EEMs) fluorescence spectra, the photo-electrochemical and photo-luminescence measurement, radical trapping test, and electron spin resonance (ESR) technique were carried out to illuminate the probable degradation pathway and mechanism of the LEV. The improved photocatalytic efficiency can be ascribed to the synergetic effect between oxygen vacancy and the Z-scheme heterojunction, which can serve as trapping centers to enhance the generation of photoexcited electrons and accelerate the charge transfer. Meanwhile, the effects of pH, photocatalyst dose, LEV concentration and different kinds of harmful organic pollutants were systematically explored from the practical application. This study offers a novel perspective for the integration of defect engineering and Z-scheme heterojunction in efficient organic pollutants degradation.

Hollow bimetal-organic framework material as solid-phase microextraction fiber coating for highly sensitive detection of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are among the most harmful persistent organic pollutants that possess high carcinogenicity and teratogenicity; hence, establishing a highly sensitive analytical method for monitoring PAHs in environmental samples is an urgent need. However, due to the low PAHs content in environmental samples and the complex matrix of the samples, it is difficult to directly determine the amount of PAHs using the existing analytical instruments. Therefore, an essential pretreatment of environmental samples should be carried out before instrumental analysis. In most pretreatment techniques, the extraction efficiency depends on the characteristics of the extraction materials. Currently, metal-organic framework materials (MOFs), which are porous materials self-assembled by metal ions and organic ligands, are used as solid-phase microextraction (SPME) coating materials for the extraction of PAHs. However, the following problems limit the application of MOFs in the SPME field: (1) MOF coating materials often require a long equilibration time for extraction because the it is difficult for the target to reach the deep adsorption sites; (2) In addition, most MOFs are formed by the coordination of single metal ions with organic monomers. The single type of open metal active sites is not conducive for realizing high extraction performance. In this study, a hollow bimetal-organic framework (H-BiMOF) was synthesized by the solvothermal method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption analysis, thermogravimetric analysis, etc. The TEM images and XRD patterns demonstrated the successful synthesis of H-BiMOF with a hollow structure, which was formed through the competitive coordination between benzoic acid and water. The H-BiMOF material showed type-Ⅳ isotherms with a surface area of 1437 m2/g and excellent thermal stability. Subsequently, a H-BiMOF-coated SPME fiber was prepared by the physical adhesion method and used to extract trace PAHs from environmental samples. Due to the hollow structure of H-BiMOF, the prepared fibers offer the advantages of high utilization of specific surface area as well as short mass transfer distance, so that the extraction process quickly reaches equilibrium. At the same time, the introduction of bimetals provides a variety of metal active sites, which improves the extraction efficiency of the fiber against electron-rich cloud targets such as PAHs. The prepared fiber also had good service life, with at least 150 cycles. Combined with gas chromatography-tandem mass spectrometry (GC-MS/MS), a new method for the determination of PAHs in environmental water samples was established. Single factor experiments were performed to investigate the effects of the SPME conditions on the analytical performance. Under the optimal conditions, the established method showed low limits of detection (0.01-0.08 ng/L), wide linear range (0.03-500.0 ng/L), good linearity (correlation coefficients≥0.9986), and acceptable reproducibility (relative standard deviations≤9.8%, n=5). Finally, typical water samples were analyzed by the established method. Four environmental water samples were collected from Dianchi Lake, Poyang Lake, Taihu Lake, and Xihu Lake in China. No benzo(a)anthracene (BaA) and chrysene (CHR) were detected in any of the water samples. However, 17.9 ng/L of fluorene (FLU) and 5.3 ng/L of phenanthrene (PHE) were found in the Poyang Lake sample; 11.3 ng/L of fluoranthene (FLA) and 24.2 ng/L of pyrene (PYR) were found in the Taihu Lake sample; 50.0 ng/L of FLU, 19.5 ng/L of PHE, 14.9 ng/L of anthracene (ANT), 34.2 ng/L of FLA, and 44.5 ng/L of PYR were found in the Xihu Lake sample. The contents of the PAHs detected in all the lake water samples were lower than the Chinese National Standard GB 5749-2006 (2000.0 ng/L). The results of this study indicate that the developed method is suitable for the sensitive detection of trace levels of PAHs in real environmental water samples.

Photocatalytic properties of a binuclear Cd-complex to different types of harmful organic pollutants

Photocatalytic properties of a binuclear Cd-complex to different types of harmful organic pollutants

Synthesis of Metal Oxide Nanoparticles using Indian Medicinal Plants for Photocatalytic Applications - A Review

The green route based on plant extracts has been regarded a valuable alternative to traditional methods for nanoparticle synthesis due to its low cost, biocompatibility, scalability, and absence of the need for additional stabilising agents during nanoparticle creation. In considerable concentrations, plant extracts contain several phytochemicals such as phenols, alkaloids, terpenoids, and tannins, as well as numerous vitamins. During the creation of metal nanoparticles from their respective precursors, these phytochemicals operate as reducing, capping, and stabilising agents. Even if photocatalytic processes are an useful technique for treating harmful organic pollutants, the bulk of present photocatalysts are unable to exploit sunlight enough to accomplish the destruction of these pollutants. According to a number of researchers, metal oxide nanoparticles have substantial photocatalytic activity when exposed to visible light. Among the several chemical and physical processes used to synthesis nanostructured metal oxide, the green synthetic pathway is the most cost-effective and eco-friendly.

Carbon-based material derived from biomass waste for wastewater treatment

Biomass waste has known as a new precursor for the production of carbon-based materials due to its carbon richness, low cost, ease to access, ubiquitous, renewable and environmental-friendliness. In this publication, the study on the availability of biomass waste and the carbon-based materials (CBMs) for wastewater treatment application is reviewed and addressed. This paper discussed several types of CBMs such as activated carbon, graphene, carbon nanotubes, biochar, and carbon aerogel. The production of these different CBMs and their modification are given special attention. As harmful organic, dyes, and inorganic pollutants emerging from the wastewater has caused damage to the environment and water supplies, adsorption is the most widely utilised conventional technology for the removal of hazardous pollutants due to its ease of use and relatively cheap in comparison with other emerging methods. This corresponds to the CBMs which mainly works on the adsorption mechanism to perform the wastewater treatment. There are three kinds of biomass waste being explained which are sewage sludge, lignocellulosic, and cotton-based waste. This paper also extensively summarised a multitude of aspects regarding the biomass waste and the CBMs derivation from biomass waste. The challenges on the synthesis of CBMs from biomass was also included. In summary, the conclusion and future direction of the research were also discussed.

A facile synthesis of visible light driven Ni3V2O8 nano-cube/BiVO4 nanorod composite photocatalyst with enhanced photocatalytic activity towards degradation of acid orange 7

Photocatalysis is one of the promising method to degrade harmful organic pollutants under visible light exposure. In this work, a novel Ni3V2O8/BiVO4 nanocomposite has been prepared by one-pot hydrothermal method, and investigated through X-ray diffraction, FT-IR, UV–visible diffuse reflectance spectroscopy, scanning and transmission electron microscopy and photoluminescence techniques. Subsequently, the photocatalytic performance of Ni3V2O8/BiVO4 nanocomposite has been examined by degrading AO7 under visible light illumination. The photocatalytic efficiency of the optimized 1:2 ratio of Ni3V2O8/BiVO4 nanocomposite photocatalyst is found to be 87% with a rate constant value of 0.03387 min−1 which are higher than those of other prepared photocatalysts. This nanocomposite exhibits excellent stability even after 3 three cycles, and shows 1.135- and 1.17-times higher photocurrent intensity than pure BiVO4 and Ni3V2O8 respectively. The mechanism for the degradation of AO7 over Ni3V2O8/BiVO4 nanocomposite photocatalyst has been proposed.

Synthesis, Characterization, and Solar Photo-Activation of Chitosan-Modified Nickel Magnetite Bio-Composite for Degradation of Recalcitrant Organic Pollutants in Water

Photocatalysis is a promising process for decomposing harmful organic pollutants in water. In this study, solar/photocatalytic degradation of two model azo dyes, i.e., methylene blue (MB) and methyl red (MR), in water usinga nanostructured chitosan-modified nickel magnetite (CS-NM) bio-composite was investigated. The CS-NM bio-composite was synthesized through a co-precipitation method and characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), thermogravimetry (TGA), and UV-Vis spectroscopy. FTIR analysis showed the uniform incorporation and conjugation of nickel magnetite (NM) into the chitosan (CS) polymer matrix. SEM showed that the average particle size was 0.5 μm. The TGA results revealed the good thermal stability of the prepared bio-composite at 300 °C. The point of zero charge was calculated as 7.5. The effect of water quality and process parameters, such as concentration of dyes, catalyst dose, solution pH, and temperatures, was investigated, for application purposes. The solar/CS-NM photocatalysis resulted in 99 and 96% degradation of individual MB and MR (C0 = 50 ppm), respectively, in 90 min. The degradation of MB and MR by solar/CS-NM photocatalysis followed pseudo-first-order kinetics, with observed rate constants (k) of 0.077 and 0.072 min−1, respectively. The CS-NM photocatalyst showed high recyclability, represented by only a 4–6% loss in the photocatalytic efficiency, after four cycles. The results showed that solar/CS-NM photocatalysis is an efficient technique for degrading recalcitrant organic pollutants, such as azo dyes, in water environments.

Photocatalytic degradation of antibiotics under various conditions

Frequent detection of antibiotics in aquatic environment represents a global ecologic problem due to the fact, that these compounds are not fully biodegradable during conventional purification processes in wastewater treatment plants. The presence of antibiotics cause that the bacteria present in water and in animal or human bodies build resistance, which can be problematic for treatment of infections. However, heterogeneous photocatalysis is a promising method for the removal of harmful organic pollutants from wastewater. In this work, a reaction rate of photocatalytic degradation of sulfathiazole was determined, using TiO2 nanopowders and TiO2 EPD layers. In the next step, the effect of the additional antibiotic presence (ampicillin) and the use of greywater as a matrix on the photocatalytic reaction was evaluated. Sulfathiazole and ampicillin were photocatalytically degraded both separately and in mixture. For the photocatalytic reactions, nanoparticles of TiO2 P25 and pure anatase in two particle sizes (5 and 100 nm) were used. The photocatalysts were added into the reaction mixture both as a free powder and immobilized by electrophoretic deposition (EPD) on stainless steel plates. The degradation kinetics was determined by HPLC analysis with UV detection. The decrease in organic carbon was monitored using a TOC instrument. Theoretical degradation products were determined by DFT calculations. Firstly, the convenience of using EPD layers was evaluated. It is necessary to filtrate or centrifuge the samples after using TiO2 suspensions, which is time and money consuming. Thus, EDP layers have a more practical use for water purification purposes. The reaction rates were comparable with both suspension and EPD photocatalysts. When sulfathiazole (10-4 M) was degraded, the reaction rate was highest with P25, followed by anatase 5 nm and anatase 100 nm. The use of EPD layers instead of free powder photocatalyst had no significant effect on the reaction rate. Furthermore, the use of immobilized photocatalyst solves problems with separating the photocatalyst from the reaction mixture after the degradation is completed. The addition of ampicillin to the reaction did not have any influence on the rate of degradation of sulfathiazole when the molar concentration was kept constant. The use of greywater instead of demineralized water for the experiments had no decreasing effect on the photocatalytic degradation of both sulfathiazole and ampicillin. The mineralization of the reaction mixture determined as a decrease in total organic carbon correlated with the results of decrease in the concentration of studied analytes. When greywater was used instead of demineralized water, it had no observable effect. In this work, the photocatalytic degradation of sulfathiazole was performed using three different TiO2 forms. The photocatalytic activity of the particles in suspensions was compared with the activity of the particles deposited on the layers. Then, the photocatalytic reaction of the solution containing the mixture of two antibiotics in demineralized water and in greywater was carried out and the mineralization under the conditions mentioned above was compared.

Photocatalytic activity of zinc oxide – graphene oxide composites

Recently, the use of various dyes in the cellulose, textile, plastics and rubber industries has resulted in severe toxic and dye contamination of wastewater. These toxic dyes are not biodegradable and have a detrimental effect on the environment, blocking sunlight and reducing photosynthesis. Consequently, there is an urgent need to develop a low-cost effective technology for purifying wastewater from harmful organic pollutants. In this context, photocatalysis is an advanced, environmentally friendly oxidation process for wastewater treatment. Recent studies have shown that the use of semiconductor photocatalytically active materials with a wide band gap is an effective method for the decomposition of organic pollutants in aqueous solutions. In this work, a low-cost technology for the synthesis of composite semiconductor zinc oxide / graphene oxide (ZnO / GO) materials by chemical deposition from an aqueous solution has been developed. The morphology, structural and photoluminescent properties of the synthesized ZnO/GO samples with different graphene oxide concentration have been studied. The research of the photocatalytic activity of synthesized zinc oxide – graphene oxide composite materials is carried out by observing an aqueous solution of rhodamine B dye degradation under ultraviolet illumination.