BiOBr and AgBr co-modified ZnO photocatalyst: A novel nanocomposite with p-n-n heterojunctions for highly effective photocatalytic removal of organic contaminants

AgBr nanoparticle surface modified SnO2 enhanced visible light catalytic performance: characterization, mechanism and kinetics study

In this study, a simple hydrothermal procedure and in situ precipitation method were used to prepare SnO2-AgBr composites, where the molar ratios of SnO2 and AgBr were 1 : 1, 1 : 2 and 2 : 1. Characterization results showed that the composites had excellent dispersion, crystallinity, and purity. A photocatalytic degradation experiment and first-order kinetic model indicate that SnO2-AgBr (1 : 1) had the best photocatalytic performance, and the degradation rates of 30 mg L-1 simulated MO and MG wastewater reached 96.71% and 93.36%, respectively, in 150 min, which were 3.5 times those of SnO2. The degradation rate of MO and MG increases with the dosage. Humic acid inhibited the degradation of MG, while a low concentration of humic acid promoted the degradation of MO, and the composite has good stability with pH. A free radical trapping experiment shows that ·OH and ·O2- were the main active substances, and h+ was the secondary one. According to the results of the characterization and photocatalysis experiments, a Z-scheme mechanism for the SnO2-AgBr composite was proposed, and the degradation pathway of target pollutants was speculated upon. This study has conceived novel methods for the development of a mature Z-scheme mechanism and in doing so has provided new approaches for the development of photocatalysis for water pollution control.

Improved Photocatalytic Activity via n-Type ZnO/p-Type NiO Heterojunctions

The design and construct pn heterojunction to reduce the recombination rate of photogenerated electron-hole pairs can effectively improve photocatalytic activity. In this study, ZnO/NiO heterojunctions were fabricated by annealing a Zn/Ni metal organic framework precursor synthesized via coprecipitation. The effects of the precursor annealing temperature on the microstructure, morphology, and optical properties of the ZnO/NiO nanocomposites were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy. The results showed that the nanocomposite was composed of hexagonal wurtzite ZnO and cubic NiO, with the former being the dominant phase. Large ZnO nanoparticles were attached to small NiO nanoparticles, and a pn heterojunction interface was formed. The photodegradation performance of the nanomaterials was evaluated by monitoring the degradation of RhB under irradiation by ultraviolet light. The ZnO/NiO nanocomposites exhibited excellent photocatalytic activity when the annealing temperature was 550 °C. The photodegradation mechanism was also analyzed in detail, revealing that the heterojunction between the n-type ZnO and the p-type NiO played an important role in impeding the recombination of photogenerated electron-hole pairs and improving the photocatalytic efficiency.

Covalent and Non-covalent Functionalized Nanomaterials for Environmental Restoration

Nanotechnology has emerged as an extraordinary and rapidly developing discipline of science. It has remolded the fate of the whole world by providing diverse horizons in different fields. Nanomaterials are appealing because of their incredibly small size and large surface area. Apart from the naturally occurring nanomaterials, synthetic nanomaterials are being prepared on large scales with different sizes and properties. Such nanomaterials are being utilized as an innovative and green approach in multiple fields. To expand the applications and enhance the properties of the nanomaterials, their functionalization and engineering are being performed on a massive scale. The functionalization helps to add to the existing useful properties of the nanomaterials, hence broadening the scope of their utilization. A large class of covalent and non-covalent functionalized nanomaterials (FNMs) including carbons, metal oxides, quantum dots, and composites of these materials with other organic or inorganic materials are being synthesized and used for environmental remediation applications including wastewater treatment. This review summarizes recent advances in the synthesis, reporting techniques, and applications of FNMs in adsorptive and photocatalytic removal of pollutants from wastewater. Future prospects are also examined, along with suggestions for attaining massive benefits in the areas of FNMs.

Advances in preparation, mechanism and applications of graphene quantum dots/semiconductor composite photocatalysts: A review

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp² carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

Microwave-assisted hydrothermal synthesis of MoS2-Ag3PO4 nanocomposites as visible light photocatalyst for the degradation of tetracycline hydrochloride

In the modern era, industrialization has facilitated the human life but produced several severe pollutants as well that are hazardous in nature. Thus the degradation of these hazardous material has drawn considerable attention. This study deals with the synthesis of MoS₂/Ag₃PO₄ heterojunction nanocomposite with 1-50% wt. using a microwave-assisted hydrothermal process as well as photocatalytic activity of tetracycline hydrochloride (TCH) degradation has been analysed. The compositional properties of nanocomposite catalysts have been studied through X-ray diffraction, Fourier transform infrared, X-ray photoelectron spectroscopy as well as structural and morphological studies were conducted through scanning electron microscopy, transmission electron microscopy, Brunauer-Emmet-Teller, photoluminescence, N₂ physical adsorption, UV-vis diffuse reflectance spectroscopy. This provides an excellent and efficient mechanism for the remediation of residual organic contaminants under visible light that could be used to decontaminate the atmosphere.

Design and Microwave-Assisted Synthesis of TiO2-Lanthanides Systems and Evaluation of Photocatalytic Activity under UV-LED Light Irradiation

The TiO2-Eu and TiO2-La systems were successfully synthesized using the microwave method. Based on the results of X-ray diffraction analysis, it was found that regardless of the analyzed systems, two crystal structures were noted for the obtained samples: anatase and rutile. The analysis, such as XPS and EDS, proved that the doped lanthanum and europium nano-particles are present only on the TiO2 surface without disturbing the crystal lattice. In the synthesized systems, there were no significant changes in the bandgap energy. Moreover, all the obtained systems were characterized by high thermal stability. One of the key objectives of the work, and a scientific novelty, was the introduction of UV-LED lamps into the metronidazole photo-oxidation pathway. The results of the photo-oxidation study showed that the obtained TiO2 systems doped with selected lanthanides (Eu or La) show high efficiency in the removal of metronidazole, and at the same consuming nearly 10 times less electricity compared to conventional UV lamps (high-pressure mercury lamp). Liquid-chromatography mass-spectrometry (LC-MS) analysis of an intermediate solution showed the presence of fragments of the degraded molecule by m/z 114, 83, and 60, prompting the formulation of a plausible photodegradation pathway for metronidazole.

Oxygen vacancy-rich 2D/0D BiO1-XBr/AgBr Z-scheme photocatalysts for efficient visible light driven degradation of tetracycline

Semiconductor-based photocatalytic technology, as a green and promising avenue in response to the abuse of antibiotic pollution and human health crisis, is restricted by the limited photo-absorption and fast recombination of photogenerated carriers. In this paper, all these challenges were settled by AgBr particles incorporated into oxygen-deficient BiOBr nanosheets, forming novel oxygen vacancy (OV)-rich 2D/0D Z-scheme heterojunctions. Z-scheme photocatalytic system has an effective separation rate of photogenerated carriers and an ability to maintain original redox capacity. Moreover, introducing OVs in the Z-scheme can not only improve the visible light absorption ability, but also serve as recombination centers, thus promoting the separation of electrons and holes. Notably, the photocatalytic activity of 2D/0D BiO_1-XBr/AgBr (2:1) was significantly improved under the irradiation of visible light, removing 81% of tetracycline after 25 min, which was about 2.62 times and 2.03 times as high as those of BiO_1-XBr and AgBr, respectively. In addition, the 2D/0D BiO_1-XBr/AgBr (2:1) indicated high photocatalytic stability and reusability, and its tetracycline degradation efficiency remained stable after five cycles. In summary, this work suggests that the photocatalysts have a great potential to remove TC and provides a possible strategy for purifying water.

Water hyacinth plant extract mediated green synthesis of Cr2O3/ZnO composite photocatalyst for the degradation of organic dye

The Cr2O3/ZnO composite catalysts with varying the amount of chromium precursors abbreviated as 0.02CrZn, 0.04CrZn, 0.06CrZn, 0.08CrZn, 0.1CrZn, and fixed the amount of Zn precursor (0.1 M) were prepared by using water hyacinth (Eichhornia crassipes) extract as a template/capping agent. The prepared catalysts were characterized and the catalytic performances of the catalysts were also checked for the degradation of methylene blue (MB) dye. The photocatalytic MB dye degradation by 0.08CrZn catalyst was achieved and 85% of MB dye was degraded within 90 min irradiation time. However, 0.1CrZ, 0.06CrZ, 0.04CrZ, 0.02CrZ, ZnO, and Cr2O3 catalysts degrade only 80, 74, 79, 76, 52, and 74% of MB dye, respectively. The catalytic performances indicated that the addition of optimum amount of chromium precursor in the preparation of Cr2O3/ZnO composite catalysts with the aid of Eichhornia crassipes plant extract enhances the catalytic activities. This performance enhancement could be as a result of reducing the electron/hole pair separation and the porosity resulted from the plant extract in the catalyst system.

Hydrothermal Synthesis of the CuWO4/ZnO Composites with Enhanced Photocatalytic Performance

Photocatalytic technology aiming to eliminate organic pollutants in water has been rapidly developed. In this work, we successfully synthesized CuWO₄/ZnO photocatalysts with different weight ratios of CuWO₄ through facile hydrothermal treatment. Crystal structures, forms, and optical properties of these as-prepared materials were investigated and analyzed. 3% CuWO₄/ZnO showed the optimum photodegradation efficiency toward methylene blue under the irradiation of simulated sunlight for 120 min, the degradation rate of which was 98.9%. The pseudo-first-order rate constant of 3% CuWO₄/ZnO was ∼11.3 and ∼3.5 times bigger than that of pristine CuWO₄ and ZnO, respectively. Furthermore, the material exhibited high stability and reusability after five consecutive photocatalytic tests. In addition, free radical capture experiments were conducted and the possible mechanism proposed explained that the synergistic effect between CuWO₄ and ZnO accelerates the photodegradation reaction. This work provides a feasible technical background for the efficient and sustainable utilization of photocatalysts in wastewater control.

A novel 0D/2D WS2/BiOBr heterostructure with rich oxygen vacancies for enhanced broad-spectrum photocatalytic performance

In this study, a novel 0D/2D WS₂/BiOBr heterostructured photocatalyst with rich oxygen vacancies was fabricated by a hydrothermal method. The WS₂ QDs/BiOBr-10 heterostructures exhibited a maximum removal rate of 92% towards ciprofloxacin (CIP) within 100 min under visible-light irradiation, which was 2.63- and 2.02- folds higher activity than that of pristine BiOBr and WS₂ QDs/BiOBr-10 with poor oxygen vacancies, respectively. In addition, the removal efficiencies of this photocatalyst towards various pollutants were 99% (Lanasol Red 5B), 95% (Rhodamine B), 85% (metronidazole), 96% (tetracycline) and 41% (Bisphenol A), respectively. Besides, the simultaneous photocatalytic degradation showed the competitive interactions between these organic contaminants for the active species, decreasing the removal efficiency for CIP. However, the simultaneous photocatalytic oxidation of CIP and reduction of Cr(VI) improved the utilization efficiency of photo-induced electrons and holes, resulting in high removal efficiencies for both CIP and Cr(VI). Three-dimensional excitation-emission matrix fluorescence spectra (3D EEMs) were used to investigate the degradation of CIP molecules. The synergistic effect of heterostructure and oxygen vacancies greatly assisted in the removal of organic pollutants, attributing to the enhanced visible-light harvesting and effective separation of photo-induced electron-hole pairs. Furthermore, trapping experiments and ESR results demonstrated that the CIP removal was dominated by the direct oxidation of holes (h⁺), whereas the hydroxyl radicals (OH) and superoxide radicals (O₂^-) acted as auxiliary active species. This study provides a new way to rationally design and construct active 0D/2D pattern heterojunction photocatalysts for environmental remediation.

Novel cadmium oxide-graphene nanocomposite grown on mesoporous silica for simultaneous photocatalytic H2-evolution

Novel Cadmium Oxide-Graphene Nanocomposite Grown on Mesoporous Silica have been successfully prepared using a self-assembly method under the catering of cetyltrimethylammonium bromide (CTAB) as the surfactant template at ambient conditions. The structural and optical properties of the obtained nanocomposites were investigated by many different techniques. The results of photocatalytic measurements revealed that almost 100% of MB organic dye was removed with the presence of SiO₂/CdO-graphene composite under visible light irradiation. Moreover, the initial pH also plays an important role in the photodegradation processes. On the other hand, this work opens a way to enhance the photocatalytic activity of gallic acid at ambient conditions without any further different oxidation processes. From the evolutionary aspect, SiO₂/CdO-graphene composite revealed better H₂ generation than that of binary photocatalyst (CdO-graphene nanocomposite). The results of characterization and photodegradation suggest that SiO₂/CdO-graphene material constitutes a new photocatalyst for the degradation of organic contaminants, as well as the development of an efficient hetero-system for hydrogen production.