Synthesis of mesoporous Ag/ZnO nanocrystals with enhanced photocatalytic activity

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

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

Improvement of the photocatalytic activity of ZnO thin films doped with manganese

In the herein report, we synthesized ZnO thin films doped with manganese (Mn). We studied the impact of Mn doping loads (1 %, 3 %, 5 % wt.) on physicochemical properties of the compounds. Furthermore, we presented the photocatalytic efficiency in removal of methylene blue dye. The structural assay indicated ZnO conserve the wurtzite crystalline structure after dopant insertion. Furthermore, the crystalline size of catalysts was reduced after dopant incorporation. The SEM analysis showed a change in surface morphology after modification of ZnO thin films. Furthermore, Raman spectroscopy verified the Mn insertion inside the ZnO lattice. After the doping process, band gap was reduced by 16 %, in comparison to bare ZnO. After the photocatalytic test, the doped catalysts showed better performance than bare ZnO in removing MB. The best test showed a kinetics constant value of 2.9 × 10-3 min-1 after 120 min of visible irradiation. Finally, the Mn(5 %):ZnO thin film was suitable after five degradation cycles, and the degradation process efficiency was reduced by 32%.

Rapid elimination of antibiotic gemifloxacin mesylate and methylene blue over Pt nanoparticles dispersed chitosan/g-C3N4 ternary visible light photocatalyst

Appropriate material selection and proper understanding of bandgap modification are key factors for the development of efficient photocatalysts. Herein, we developed an efficient, well-organized visible light oriented photocatalyst based on g-C₃N₄ in association with polymeric network of chitosan (CTSN) and platinum (Pt) nanoparticles utilizing a straightforward chemical approach. Modern techniques like XRD, XPS, TEM, FESEM, UV-Vis, and FTIR spectroscopy were exploited for characterization of synthesized materials. XRD results confirmed the involvement of α-polymorphic form of CTSN in graphitic carbon nitride. XPS investigation confirmed the establishment of trio photocatalytic structure among Pt, CTSN, and g-C₃N₄. TEM examination showed that the synthesized g-C₃N₄ possesses fine fluffy sheets like structure (100 to 500 nm in size) intermingled with a dense layered framework of CTSN with good dispersion of Pt nanoparticles on g-C₃N₄ and CTSN composite structure. The bandgap energies for g-C₃N₄, CTSN/g-C₃N₄, and Pt@ CTSN/g-C₃N₄ photocatalysts were found to be 2.94, 2.73, and 2.72 eV, respectively. The photodegradation skills of each created structure have been examined on antibiotic gemifloxacin mesylate and methylene blue (MB) dye. The newly developed Pt@CTSN/g-C₃N₄ ternary photocatalyst was found to be efficacious for the elimination of gemifloxacin mesylate (93.3%) in 25 min and MB (95.2%) just in 18 min under visible light. Designed Pt@CTSN/g-C₃N₄ ternary photocatalytic framework exhibited ⁓ 2.20 times more effective than bare g-C₃N₄ for the destruction of antibiotic drug. This study provides a simple route towards the designing of rapid, effective visible light oriented photocatalyts for the existing environmental issues.

Ag nanoparticle-decorated chitosan/SrSnO3 nanocomposite for ultrafast elimination of antibiotic linezolid and methylene blue

Effective design of ultrafast new-generation photocatalysts is a challenging task that requires highly dedicated efforts. This research focused on the development and design of ultrafast smart ternary photocatalysts containing SrSnO₃ nanostructures in conjugation with chitosan (CTSN) and silver (Ag) nanoparticles by a very simple and straightforward methodology. Modern analytical tools such as FESEM, TEM, XRD, XPS, FTIR, and UV-Vis spectroscopy were employed to characterize the synthesized nanostructures. XRD and XPS analysis confirmed the successful creation of ternary organization among the Ag, CTSN, and SrSnO₃. The TEM images clearly confirmed that CTSN possessed overlapping micron-sized sheets with a layered morphology, whereas the undoped SrSnO₃ particles exhibited spherical and elongated shapes and particle sizes ranging from 20 to 80 nm. These particles were produced in high density with homogeneously distributed Ag nanoparticles (4-15 nm). The bandgap energy (E_g) for bare SrSnO₃, CTSN/SrSnO₃, and Ag@CTSN/SrSnO₃ nanocomposites was found to be 4.0, 3.94, and 3.7 eV, respectively. The photocatalytic efficiencies of all newly created photocatalysts were evaluated by considering an antibiotic linezolid drug and methylene blue (MB) dye molecule as target analytes. Among all investigated samples, the Ag@CTSN/SrSnO₃ photocatalyst was found to be highly superior, with ultrafast removal of the linezolid drug at 96.02% within 25 min and almost total removal of the MB dye in just 12 min under UV light irradiation. The Ag@CTSN/SrSnO₃ photocatalyst exhibited removal rate that was 3.36 times faster than that of bare SrSnO₃. The present report delivers a highly promising, extremely efficient, and very simple, straightforward treatment methodology for the effective destruction of lethal and notorious pollutants, enabling the appropriate management of current environmental concerns.

Nanocomposite ZnO/g-C3N4 for Improved Degradation of Dyes under Visible Light: Facile Preparation, Characterization, and Performance Investigations

In this study, ZnO/g-C3N4 nanocomposites were prepared via a physical mixing-calcination process for improved degradation of dyes under visible light irradiation. The BET surface area, pore volume, crystal size, and pHpzc of the ZnO/g-C3N4 composite were 3.9 m2/g, 0.034 cm3/g, 18.1 nm, and 7.7, respectively. Although the morphology of the ZnO/g-C3N4 composite was very different from that of pure g-C3N4, their average pore sizes were similar. The Eg of the ZnO/g-C3N4 composite (3.195 eV) was slightly lower than that of ZnO (3.195) but much higher than that of g-C3N4 (2.875). The interface interaction of ZnO and g-C3N4, which was revealed by oscillations of Zn-C, benefited the transport of photoinduced charge carriers and reduced the recombination of electron-hole. As the result, the ZnO/g-C3N4 composite had higher photocatalytic activity than ZnO and g-C3N4. Its degradation efficiency (DE) value for methylene blue (MB) in 90 min and rate constant were 93.2 % and 0.025 min‑1, respectively. In addition, the effects of ZnO/urea molar ratio, catalyst dosage, solution pH, and concentration of dye on photocatalytic degradation of MB were completely investigated. The photocatalytic performance of the ZnO/g-C3N4 composite was evaluated by the degradation of other persistent organic compounds, also compared to other catalysts in the literatures. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Synergistic influence of FRET, bulk recombination centers, and charge separation in enhancing the visible-light-driven photocatalytic activity of Cu2+-ion-doped ZnO nanoflowers

Pure ZnO and a group of Cu²⁺-ion-doped (4, 6, and 8 wt%) ZnO nanomaterials are synthesized using the co-precipitation technique. X-ray diffraction and Fourier transform infrared spectroscopy confirm both the substitution of Zn²⁺ ions by Cu²⁺ ions in the ZnO lattice and formation of the ZnO/CuO composite. The divalent oxidation state of Cu is confirmed using X-ray photoelectron spectroscopy. A suppression in the oxygen vacancy density is observed up to a doping level of 6 wt%, but beyond that it increases. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show a cross-linked nanoflower-like structure. The presence of a separate CuO phase is also confirmed via TEM. Absorption spectroscopy yields a reduction in the bandgap up to 6 wt%, after which it is increased for 8 wt%. An enhanced plasmon band in the spectra reveals the presence of CuO. The photoluminescence is quenched for doping up to 6 wt%, and with further doping the emission is enhanced. These observations are explained by the doping-concentration-dependent Förster resonance energy transfer (FRET) phenomenon between the ZnO (donor) and the CuO (acceptor). For the highest doping concentration, the emission profile shows a sudden enhancement resulting from the simultaneous competition of two FRET mechanisms (the intra-acceptor mechanism and the inter-donor-acceptor mechanism). By contrast, for other doped nanomaterials, the inter-donor-acceptor FRET mechanism with doping-concentration dependence is able to explain the suppression of the emission intensity. All doped nanomaterials show an improved visible-light-driven photocatalytic efficiency compared with pure ZnO for methylene blue, which results from the synergistic effects of a reduction in the concentration of bulk defects, enhanced charge separation, and FRET. The highest photocatalytic performance is demonstrated by the 6 wt% nanomaterial due to its optimum doping concentration. However, beyond this concentration, the formation of excessive CuO on the surface of ZnO increases the concentration of bulk defects, and the simultaneous occurrence of the inter-donor-acceptor FRET and intra-acceptor FRET mechanisms takes place leading to the rapid recombination of electron-hole pairs and reduced photocatalytic activity.

Preparation of Hierarchical Structure Au/ZnO Composite for Enhanced Photocatalytic Performance: Characterization, Effects of Reaction Parameters, and Oxidizing Agent Investigations

Zinc oxide (ZnO) has been shown as a potential photocatalyst under ultraviolet (UV) light but its catalytic activity has a limitation under visible (Vis) light due to the wide bandgap energy and the rapid recombination of electrons and holes. Thus, hierarchical structure Au/ZnO composites were fabricated by the hydrothermal method and chemical reduction method for enhanced photocatalytic performance under visible light. As-prepared composites were characterized by UV-vis diffuse reflectance spectra (DR/UV-Vis), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and electron paramagnetic resonance (EPR). The Au/ZnO-5 composite showed the highest adsorption among as-prepared samples in the range of 250-550 nm, having bandgap energy of 0.13 eV. Au nanoparticles of about 3-5 nm were well dispersed on hierarchical flower ZnO with approximately 10-15 μm. The EPR signal at $g=1.965$ on both ZnO and Au/ZnO samples was attributed to oxygen vacancy Vo•, but the presence of Au led to a decrease in signal strength of Au/ZnO composite, showing the degradation efficiency (DE) and reaction rate of 99.2% and 0.109 min-1, respectively; these were larger than those of other samples. The effects of reaction parameters and oxidizing agents on photocatalytic performance were investigated and showed that the presence of H2O2 and O2 could improve the reaction of composite. In addition, the kinetic and photocatalytic mechanism of tartrazine (TA) on catalysts were studied by the first-order kinetic model and characterized analyses.

Highly Dispersed Pt Nanoparticle-Doped Mesoporous ZnO Photocatalysts for Promoting Photoconversion of CO2 to Methanol

Photoreduction of CO₂ is considered a challenge due to the lack of effective photocatalysts with wide-spectrum absorption, active charge separation dynamically, and CO₂ adsorption. Herein, mesoporous Pt/ZnO nanocomposites with different Pt percentages (0.5-2%) have been fabricated using the sol-gel process in the presence of a template for CO₂ photoreduction during visible-light exposure. Pt nanoparticles (NPs) deposited onto mesoporous ZnO with a considerable surface area can effectively promote charge mobility. The mesoporous 1.5% Pt/ZnO nanocomposite exhibits an optimal CH₃OH yield (668 μmol g^-1), which is 18.5-fold larger than that of mesoporous ZnO (36 μmol g^-1). The most photoactive material was the 1.5% Pt/ZnO nanocomposite, producing CH₃OH of 668 μmol g^-1, and the production rate of CH₃OH over the 1.5% Pt/ZnO nanocomposite (74.11 μmol g^-1 h^-1) was increased 20 times in comparison with ZnO NPs (3.72 μmol g^-1 h^-1). The enhancement of CO₂ photoreduction efficiency over Pt/ZnO nanocomposites was attributed to the formation of the heterojunction at the Pt/ZnO interface, promoting a lower resistance to charge transfer and a larger electron transfer to the conduction band. Mesoporous Pt/ZnO nanocomposites offer enhanced accessibility and a larger surface area. Such an unparalleled mesostructure provides a new framework for the construction and design of photoactive materials with high-efficiency photocatalysts.

Fabrication of Mesoporous PtO-ZnO Nanocomposites with Promoted Photocatalytic Performance for Degradation of Tetracycline

Herein, we report a simple incorporation of PtO NPs at diverse percentages (0.2-0.8 wt %) onto a highly crystalline and mesoporous ZnO matrix by the wet-impregnation approach for degradation of tetracycline (TC) upon visible light exposure. These well-dispersed and small-sized PtO NPs provide the mesoporous PtO-ZnO nanocomposites with outstanding photocatalytic performance for complete TC degradation. The optimized 0.6% PtO-ZnO photocatalyst exhibits excellent TC degradation, and its degradation efficiency reached ∼99% within 120 min. The photocatalytic performance of the 0.6% PtO-ZnO nanocomposite is 20 and 10 times higher than that of pristine ZnO and commercial P-25, respectively. The photodegradation rate of TC over the 0.6% PtO-ZnO nanocomposite is 34 and 12.5 times greater than that of pristine ZnO and commercial P-25, respectively. This is because of the large surface area, unique porous structure, synergistic effect, and broad visible light absorption of the PtO-ZnO nanocomposite. Moreover, mesoporous PtO-ZnO nanocomposites showed a high stability and recyclability over five iterations. This work demonstrates the remarkable role of combining PtO and ZnO photocatalysts in providing nanocomposites with significant potential for the preservation of human health through wastewater remediation.

Silver nanoparticles decorated magnetic polymer composites (Fe3O4@PS@Ag) as highly efficient reusable catalyst for the degradation of 4-nitrophenol and organic dyes

A facile and cost-effective preparation of silver nanoparticles decorated magnetic composite for the effective catalytic degradation of 4-nitrophenol (4-NP) and Methylene blue (MB) and Rhodamine B (RhB) was investigated. Fe₃O₄@Polystyrene@Ag (Fe₃O₄@PS@Ag) catalyst was prepared via a two-step procedure. Firstly, carboxyl groups modified magnetic microspheres (Fe₃O₄@PS-COOH) has been successfully synthesized by microemulsion polymerization. Then Ag ions were adsorbed and in-situ reduced on the surface of Fe₃O₄@PS microspheres. To estimate the catalytic activity of Fe₃O₄@PS@Ag catalyst, the reduction experiments of MB, RhB and 4-NP were performed in the presence of NaBH₄. The results indicated that Fe₃O₄@PS@Ag catalyst has a good catalytic performance and these dyes can be reduced in a very short time, which the apparent rate coefficients are 0.0089 s^-1, 0.0187 s^-1 and 0.0086 s^-1 for MB, RhB and 4-NP respectively. In addition, it could be easily collected from aqueous solution by a magnet so that the catalyst could be recovered and reused after the catalytic process. The catalytic activity was still high after seven cycles. This catalytic reaction is in agreement with the pseudo-first-order kinetic equation. Furthermore, the as-prepared Fe₃O₄@PS@Ag catalyst outperforms other catalysts in the degradation of these organic dyes.

Facile Synthesis of Mesoporous Ag2O-ZnO Heterojunctions for Efficient Promotion of Visible Light Photodegradation of Tetracycline

Fabrication of 3D mesoporous Ag₂O-ZnO heterojunctions at varying Ag₂O contents has been achieved through poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (Pluronic F-108) as the structure-directing agent for the first time. The mesoporous Ag₂O-ZnO nanocomposites exhibited a mesoporous structure, which revealed a large pore volume and high surface area. The photocatalytic efficiency over mesoporous Ag₂O-ZnO nanocomposites for tetracycline (TC) compared with that over commercial P-25 and pristine ZnO NPs through the visible light exposure was studied. Mesoporous 1.5% Ag₂O-ZnO nanocomposites indicated the highest degradation efficiency of 100% of TC during 120 min of the visible light exposure compared with 5% and 10% for pristine ZnO NPs and commercial P-25, respectively. The TC degradation rate took place much rapidly over 1.5% Ag₂O-ZnO nanocomposites (0.798 μmol L^-1 min^-1) as compared to either commercial P-25 (0.097 μmol L^-1 min^-1) or ZnO NPs (0.035 μmol L^-1 min^-1). The mesoporous 1.5% Ag₂O-ZnO nanocomposite revealed the highest degradation rate among all synthesized samples, and it was 23 and 8 orders of magnitudes greater than those of pristine ZnO NPs and P-25, respectively. The photoluminescence and transient photocurrent intensity behaviors have been discussed to explore photocatalysis mechanisms. It is anticipated that the present work will contribute some suggestions for understanding other heterojunctions with outstanding behaviors.

Comparative Study of ZnO Thin Films Doped with Transition Metals (Cu and Co) for Methylene Blue Photodegradation under Visible Irradiation

We synthesized and characterized both Co-doped ZnO (ZnO:Co) and Cu-doped ZnO (ZnO:Cu) thin films. The catalysts’ synthesis was carried out by the sol–gel method while the doctor blade technique was used for thin film deposition. The physicochemical characterization of the catalysts was carried out by Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, and diffuse reflectance measurements. The photocatalytic activity was studied under visible irradiation in aqueous solution, and kinetic parameters were determined by pseudo-first-order fitting. The Raman spectra results evinced the doping process and suggested the formation of heterojunctions for both dopants. The structural diffraction patterns indicated that the catalysts were polycrystalline and demonstrated the presence of a ZnO wurtzite crystalline phase. The SEM analysis showed that the morphological properties changed significantly, the micro-aggregates disappeared, and agglomeration was reduced after modification of ZnO. The ZnO optical bandgap (3.22 eV) reduced after the doping process, these being ZnO:Co (2.39 eV) and ZnO:Co (3.01 eV). Finally, the kinetic results of methylene blue photodegradation reached 62.6% for ZnO:Co thin films and 42.5% for ZnO:Cu thin films.

Highly efficient catalytic/sonocatalytic reduction of 4-nitrophenol and antibacterial activity through a bifunctional Ag/ZnO nanohybrid material prepared via a sodium alginate method

In this work, a bifunctional nanohybrid silver/zinc oxide material (Ag/ZnO) has been synthesized by a rapid route using sodium alginate simultaneously as a sacrificial template and silver reducing agent. The obtained samples were characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid diffuse reflectance and liquid state UV-visible spectroscopy (DRS, UV-visible), and nitrogen adsorption-desorption analysis (BET-BJH). The XRD patterns showed that the Ag/ZnO sample is composed of a hexagonal zinc oxide structure with cubic metallic silver (Ag°). SEM micrographs exhibited a porous structure which was confirmed by BET-BJH methods to be mesoporous. The Ag/ZnO material was used as a nanocatalyst in the conversion of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as well as an antibacterial agent against Escherichia coli and Staphylococcus aureus. It was found that an efficient 4-NP reduction to 4-AP in the presence of NaBH₄ shows a rate constant of 0.418 min^-1 under ultrasonic energy and 0.316 min^-1 without ultrasonic energy. Both the catalysis reaction and antibacterial activity analysis were conducted in water solution and showed a synergetic effect of metallic silver loading.

Crystal phase induced band gap energy enhancing the photo-catalytic properties of Zn–Fe2O4/Au NPs: experimental and theoretical studies

Au NPs on ZnFe₂O₄ enhances visible absorption, employed for paracetamol oxidation, where peaks were resolved by 2D HPLC.

Electrochemically active biofilm-assisted biogenic synthesis of an Ag-decorated ZnO@C core–shell ternary plasmonic photocatalyst with enhanced visible-photocatalytic activity

An Ag–ZnO@C core–shell ternary photocatalyst was synthesized via a bio-catalytic route for photocatalytic degradation of RhB and 4-NP under visible light.

Implantation of Fe3O4 Nanoparticles in Shells of Au@m-SiO2 Yolk@Shell Nanocatalysts with Both Improved Recyclability and Catalytic Activity

Multifunctional nanocatalysts of Au@Fe₃O₄/m-SiO₂ yolk@shell hybrids had been developed through a template-assisted synthesis, where Fe₃O₄ nanoparticles (∼12 nm) and m-SiO₂ shells were sequentially assembled on surfaces of Au/SiO₂ core/shell templates, followed by selective etching of the inner SiO₂ cores, leading to the formation of Au@Fe₃O₄/m-SiO₂ yolk@shell hybrids. The Fe₃O₄ nanoparticles were implanted in the inner surfaces of m-SiO₂ shells with partially exposed surfaces to the inner cavity. The novel design not only ensures a high surface area (540.0 m²/g) and saturation magnetization (48.6 emu/g) of the hybrids but also enables interaction between Au and Fe₃O₄ nanoparticles. Catalytic tests toward the reduction of 4-nitrophenol in the presence of NaBH₄ indicated that Au@Fe₃O₄/m-SiO₂ yolk@shell nanocatalysts not only showed high stability and recyclability but also maintained improved catalytic activity as a result of the synergetic effect resulting from Au and Fe₃O₄ interactions.

Facet-Dependent Photoreduction on Single ZnO Crystals

Photocatalytic reactions occur at the crystal-solution interface, and hence specific crystal facet expression and surface defects can play an important role. Here we investigate the structure-related photoreduction at zinc oxide (ZnO) microparticles via integrated light and electron microscopy in combination with silver metal photodeposition. This enables a direct visualization of the photoreduction activity at specific crystallographic features. It is found that silver nanoparticle photodeposition on dumbbell-shaped crystals mainly takes place at the edges of O-terminated (0001̅) polar facets. In contrast, on ZnO microrods photodeposition is more homogeneously distributed with an increased activity at {101̅1̅} facets. Additional time-resolved measurements reveal a direct spatial link between the enhanced photoactivity and increased charge carrier lifetimes. These findings contradict previous observations based on indirect, bulk-scale experiments, assigning the highest photocatalytic activity to polar facets. The presented research demonstrates the need for advanced microscopy techniques to directly probe the location of photocatalytic activity.

Recent advances in nanomaterials for water protection and monitoring

Nanomaterials (NMs) for adsorption, catalysis, separation, and disinfection are scrutinized. NMs-based sensor technologies and environmental transformations of NMs are highlighted.

Enhanced Photocatalytic Activity of Ag Doped ZnO Nanorods for Degradation of an Azo Dye

  In this study, Ag-ZnO nanophotocatalyst has been synthesized through microemulsion technique and the effect of silver modification on ZnO nanorods has been evaluated. The photocatalytic activity of nanocatalyst was examined by degradation of Acid Yellow 23 (AY23) as a model of mono azo dye under UV illumination. Ag-ZnO catalyst was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS) and diffuse reflectance spectroscopy (DRS) analysis. The degradation of AY23 was studied under different operational parameters. Results show that the photocatalytic reaction followed the pseudo-first-order kinetic. The highest photocatalytic degradation of 20 mg/L AY23 dye solution under UV irradiation (light intensity = 50 W/m2 , [Ag-ZnO]0 = 400 mg/L with 2 wt% Ag doped ZnO, calcined at 450 °C) was about 93.3% during 30 minutes of reaction that shows an enhancement in comparison to pure ZnO which was 65.48%.

High-efficiency sono-solar-induced degradation of organic dye by the piezophototronic/photocatalytic coupling effect of FeS/ZnO nanoarrays

Highly-efficient sono-solar-induced degradation of organic dye by the piezophototronic/photocatalytic coupling effect of FeS/ZnO nanoarrays was achieved. A steel screen was used as the substrate for supporting FeS/ZnO nanoarrays, and the nanoarrays were vertically and uniformly grown on the substrate via a wet-chemical route. Under ultrasonic and solar irradiation, FeS/ZnO nanoarrays have high sono-photocatalytic activity for degrading methylene blue in water. The photogenerated carriers can be separated by a piezoelectric field and a built-in electric field, resulting in a low recombination rate and high photocatalytic efficiency. The piezophototronic and photocatalytic effects were coupled together. The experimental/theoretical data indicate that this novel wastewater treatment can co-use mechanical and solar energy in nature, and so is a promising technology for environment improvement.

Photocatalytic activity of π-conjugated conducting polymer microspheres from ultrasonic spray pyrolysis

Conductive polymers have considerable interest on degradation of pollutants from textile wastewaters and appear as a new class of active photocatalysts under visible light. Poly(3,4-ethylenedioxythiophene) (PEDOT), as one of π-conjugated conducting polymer microspheres, is highly efficient catalyst in textile pollutant degradation. Ultrasonic spray pyrolysis method was used to produce spherical PEDOT particles in one step. The novel PEDOT-based photocatalysts are very stable with cycling and can be reused without appreciable loss of activity. Ag–ZnO nanocatalysts are not effective photocatalysts as compared to highly porous microspheres of PEDOT. After 240 min total processing time for the solution of phenol and RR180 under Vis irradiation, the performances of 71.6% and 78.2% for degradation and 68.3% for total organic carbon removal of RR180 were reached in the presence of the porous PEDOT photocatalysts.

Silver-functionalized g-C3N4 nanohybrids as signal-transduction tags for electrochemical immunoassay of human carbohydrate antigen 19-9

A simple and feasible electrochemical immunosensing platform was developed for highly efficient screening of a disease-related protein (human carbohydrate antigen 19-9, CA 19-9 used in this case) using silver-functionalized g-C3N4 nanosheets (Ag/g-C3N4) as signal-transduction tags. Initially, Ag/g-C3N4 nanohybrids were synthesized by combining thermal polymerization of the melamine precursor with the photo-assisted reduction method. Thereafter, the as-synthesized Ag/g-C3N4 nanohybrids were utilized for the labeling of the anti-CA 19-9 detection antibody by using a typical carbodiimide coupling method. The assay was carried out on a capture antibody-modified glassy carbon electrode in a sandwich-type detection mode. The detectable signal mainly derived from the voltammetric characteristics of the immobilized nanosilver particles on the g-C3N4 nanosheets within the applied potentials. Under the optimal conditions, the voltammetric peak currents increased with the increasing amount of target CA 19-9, and exhibited a wide linear range from 5.0 mU mL(-1) to 50 U mL(-1) with a detection limit of 1.2 mU mL(-1). Our strategy also displayed good reproducibility, precision and specificity. The results of the analysis of clinical serum specimens were in good accordance with the results obtained by an enzyme-linked immunosorbent assay (ELISA) method. The newly developed immunosensing system is promising for enzyme-free and cost-effective analysis of low-abundance proteins.

Review on ZnO hybrid photocatalyst: impact on photocatalytic activities of water pollutant degradation

Zinc oxide (ZnO) is one of the most widely used benchmark standard photocatalysts in the field of environmental applications. However, the large band gap of ZnO and the massive recombination of photogenerated charge carriers, especially in its nanosize, limit the overall photocatalytic efficiency. This can be further overcome by modifying the electronic band structure of ZnO by hybridization with a narrow band gap material, including metal, metal oxide, carbon based, and polymeric based. Indeed, ZnO hybridization with the respective materials contributed to its sensitizer by shifting the absorption wavelength to the visible region of the spectrum. This review encompasses several advancements made in the mentioned aspects, and also some of the new physical insights related to the charge transfer events, such as charge carrier generation, trapping, detrapping, and their transfer to surface, are discussed for each strategy of the hybrid ZnO. The synergistic effects in the mixed polymorphs of ZnO and also the theories proposed for their enhanced activity are reported. The review also highlights the potential application of ZnO hybrid for different kinds of pollutants from different wastewater sources.