New insight into ZnO@ZIFs composite: an efficient photocatalyst with boosted light response ability and stability for CO2 reduction

One of the main causes of climate change and energy exhaustion is the excessive use of fossil fuels. Photocatalytic carbon dioxide (CO₂) reduction technology uses inexhaustible sunlight to directly convert CO₂ into value-added chemicals or fuels not only solving the problem of greenhouse effect but also alleviating the shortage of fossil energy. In this work, a well-integrated photocatalyst is synthesized through growing zeolitic imidazolate frameworks (ZIFs) with different metal nodes on ZnO nanofiber (NFs) for CO₂ reduction. One-dimensional (1D) ZnO NFs have better CO₂ conversion efficiency due to the high surface-to-volume ratio and low light reflectivity. 1D nanomaterials with superior aspect ratios can be assembled into free-standing flexible membranes. In addition, it has been found that ZIFs nanomaterials with bimetallic nodes not only have better CO₂ reduction capabilities but also exhibit superior thermal and water stability. The photocatalytic CO₂ conversion efficiency and selectivity of ZnO@ZCZIF are shown to be significantly enhanced which can be attribute to the strong CO₂ adsorption/activation, efficient light capture, excellent electron-hole pair separation efficiency, and specific metal Lewis sites. This work provides insights into the rational construction of well-integrated composite materials to improve the photocatalytic carbon dioxide reduction performance.

Microwave-assisted preparation of Ag/Fe magnetic biochar from clivia leaves for adsorbing daptomycin antibiotics

Novel clivia biochar adsorbing daptomycin (DAP) was prepared by microwave digestion–anaerobic carbonization in this work. Fe/Ag submicron particles were introduced to the biochar surface based on the reducibility of biochar to enhance its adsorption capacity. Characterization confirmed that modified biochar (AF-biochar) had a higher particle size (126 μm), larger specific surface area (521.692 m2 g−1), richer pore structure, and higher thermal stability. The effects of the main variables (e.g., the solution pH, contact time, initial DAP concentration, and temperature) were investigated during adsorption. The results showed that AF-biochar could reach the adsorption equilibrium at pH 4.8 for 85 min. Besides, the adsorption capacity was 48.25 mg g−1, and the adsorption efficiency was 96.50% when the concentration of DAP was 25 mg L−1. The pseudo-second-order kinetics (R 2 = 0.9997), Langmuir equation (R 2 = 0.9999), and thermodynamics (R 2 = 0.9631) of AF-biochar fit well, indicating that the main adsorption process of AF-biochar was spontaneous, exothermic, and monolayer. Their adsorption was analyzed by physical and chemical adsorption. The main adsorption mechanisms included the electron donor–acceptor interaction, electrostatic force interaction, Lewis acid–base interaction, and H-bond interaction.

Evaluation of N doped rGO-ZnO-CoPc(COOH)8 nanocomposite in cyanide degradation and its bactericidal activities

In the present study, an attempt has been made to design a solar light driven N-rGO-ZnO- CoPc(COOH)₈ nanocomposite for the degradation of cyanide. The morphological and structural characterization of the synthesized nanocomposite was performed by XRD, FT-IR, XPS, UV-vis DRS, FESEM, TEM, EDS, PL spectra and BET surface area. The results revealed that almost 91% degradation and 86% toxicity removal occurred at 25 mgL^-1 of initial cyanide concentration by the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite under illumination of solar light within 120 min. Analysis of free radicals reveals that the generation of OH^. radicals was the predominant species in the photocatalytic degradation process. The cyanide degradation follows pseudo-first order kinetics. The estimated apparent rate constant (K_app) of the above nanocomposite was 3 times higher than that of the ZnO photocatalyst alone together with a very good recycle activities. This might be due to the application of metallpthalocyanine photosensitizer CoPc(COOH)₈ which enhances the rate of visible light absorption efficiency and activates the higher band gap ZnO photocatalyst under visible light. In addition, the presence of residual oxygen in N-rGO also promotes nucleation and anchor sites for interfacial contact between ZnO and N-rGO for effective charge transfer. Further, the N-rGO-ZnO-CoPc(COOH)₈ photocatalytic system showed significant antibacterial activities against mixed culture systems. Therefore, the N-rGO-ZnO-CoPc(COOH)₈ nanocomposite may be an alternative solar light driven photocatalyst system for the removal of cyanide from the wastewater along with its strong disinfectant activities.

Self-Assembled Silver Nanoparticles Decorated on Exfoliated Graphitic Carbon Nitride/Carbon Sphere Nanocomposites as a Novel Catalyst for Catalytic Reduction of Cr(VI) to Cr(III) from Wastewater and Reuse for Photocatalytic Applications

Silver nanoparticles decorated on an exfoliated graphitic carbon nitride/carbon sphere (AgNP/Eg-C₃N₄/CS) nanocomposites were synthesized by an adsorption method with a self-assembled process. These nanoparticles were characterized by different techniques like UV-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Raman spectroscopy, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), electrochemical impedance spectroscopy (EIS), and ζ potential. AgNP/Eg-C₃N₄/CS nanocomposites showed a higher catalytic reduction activity for the conversion of Cr(VI) into Cr(III) with formic acid (FA) at 45 °C when compared to bulk graphitic carbon nitride (Bg-C₃N₄, Eg-C₃N₄, CS, and Eg-C₃N₄/CS). The kinetic rate constants were determined as a function of catalyst dosage, concentration of Cr(VI), pH, and temperature for the AgNP/Eg-C₃N₄/CS nanocomposite. This material showed higher reduction efficiency (98.5%, k = 0.0621 min^-1) with turnover frequency (0.0158 min^-1) for the reduction of Cr(VI) to Cr(III). It also showed great selectivity and high stability after six repeated cycles (98.5%). Further, the reusability of the Cr(III)-AgNP/Eg-C₃N₄/CS nanocomposite was also investigated for the photocatalytic degradation of methylene blue (MB) under visible light irradiation with various time intervals and it showed good degradation efficiency (α = 97.95%). From these results, the AgNP/Eg-C₃N₄/CS nanocomposite demonstrated higher catalytic activity, improved environmental friendliness, lower cost for the conversion of toxic Cr(VI) to Cr(III) in solutions, and also good reusability.

Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review

Over the last few years, industrial and anthropogenic activities have increased the presence of organic pollutants such as dyes, herbicides, pesticides, analgesics, and antibiotics in the water that adversely affect human health and the environment worldwide. Photocatalytic treatment is considered a promising, economical, effective, and sustainable process that utilizes light energy to degrade the pollutants in water. However, certain drawbacks like rapid recombination and low migration capability of photogenerated electrons and holes have restricted the use of photo-catalysts in industries. Hence, despite the abundance of lab-scale research, the technology is still not much commercialized in the mainstream. Several structural modifications in the photo-catalysts have been adopted to enhance the pollutant degradation performance to overcome the same. In this context, the present review article outlines the different advanced heterostructures synthesized to date for improved degradation of three major organic pollutants: antibiotics, dyes, and pesticides. Moreover, the article also emphasizes the degradation kinetics of photo-catalysts and the publication trend in the past decade along with the roadblocks preventing the transfer of technology from the laboratory to industry and new age photo-catalysts for the profitable implications in industrial sectors.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

Review on the Visible Light Photocatalysis for the Decomposition of Ciprofloxacin, Norfloxacin, Tetracyclines, and Sulfonamides Antibiotics in Wastewater

Antibiotics are chemical compounds that are used to kill or prevent bacterial growth. They are used in different fields, such as the medical field, agriculture, and veterinary. Antibiotics end up in wastewater, which causes the threat of developing antibacterial resistance; therefore, antibiotics must be eliminated from wastewater. Different conventional elimination methods are limited due to their high cost and effort, or incomplete elimination. Semiconductor-assisted photocatalysis arises as an effective elimination method for different organic wastes including antibiotics. A variety of semiconducting materials were tested to eliminate antibiotics from wastewater; nevertheless, research is still ongoing due to some limitations. This review summarizes the recent studies regarding semiconducting material modifications for antibiotic degradation using visible light irradiation.

Emerging Hybrid Nanocomposite Photocatalysts for the Degradation of Antibiotics: Insights into Their Designs and Mechanisms

The raising occurrence of antibiotics in the global water bodies has received the emerging concern due to their potential threats of generating the antibiotic-resistive and genotoxic effects into humans and aquatic species. In this direction, the solar energy assisted photocatalytic technique offers a promising solution to address such emerging concern and paves ways for the complete degradation of antibiotics with the generation of less or non-toxic by-products. Particularly, the designing of hybrid photocatalyticcomposite materials has been found to show higher antibiotics degradation efficiencies. As the hybrid photocatalysts are found as the systems with ideal characteristic properties such as superior structural, surface and interfacial properties, they offer enhanced photoabsorbance, charge-separation, -transfer, redox properties, photostability and easy recovery. In this context, this review study presents an overview on the recent developments in the designing of various hybrid photocatalytic systems and their efficiency towards the degradation of various emerging antibiotic pharmaceutical contaminants in water environments.

Construction of hollow ZnO/Mn-ZIF-67 heterojunction photocatalysts: enhanced photocatalytic performance and mechanistic insight

Thanks to the unique structure and properties of MOFs, a well-designed novel hollow ZnO/Mn-ZIF-67 composite photocatalyst was synthesized by a facile sonocrystallization approach successfully.

Synergistic adsorption-photocatalytic degradation effect and norfloxacin mechanism of ZnO/ZnS@BC under UV-light irradiation

Norfloxacin (NOF) is an environmentally harmful and ubiquitous aquatic pollutant with extensive production and application. In this study, a novel composition named carbon-based composite photocatalytic material of zinc oxide and zinc sulphide (ZnO/ZnS@BC) was successfully obtained by the impregnation-roasting method to remove NOF under UV-light. Scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive spectrometer characterised the composition. ZnO/ZnS was successfully decorated on the surface of biochar (BC). The pH, the ZnSO₄/PS ratio, and ions and quenchers, were investigated. High removal efficiency was obtained with a pH of 7 and a ZnSO₄/PS ratio of 1:1, and the removal ratio of NOF reached 95% within three hours; the adsorption and degradation ratios reached 46% and 49%, respectively. Fe²⁺ promoted the degradation of NOF, whereas other ions inhibited it, with NO₃^- showing the strongest inhibitory effect. Three reactive species (tert-butanol, quinone, and ammonium oxala) were identified in the catalytic system. The decreasing order of the contribution of each reactive species was: O₂^- > ·OH^- > h⁺. Additionally, a recycling experiment demonstrated the stability of the catalyst; the catalytic degradation ratio of NOF reached 78% after five successive runs. Therefore, ZnO/ZnS@BC possessed strong adsorption capacity and high ultraviolet photocatalysis ability.

Preparation of a novel Z-scheme KTaO3/FeVO4/Bi2O3 nanocomposite for efficient sonocatalytic degradation of ceftriaxone sodium

In this work, a novel Z-scheme sonocatalyst, KTaO₃/FeVO₄/Bi₂O₃, is prepared via ultrasonic-assisted isoelectric point method. The prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The catalytic activity of Z-scheme KTaO₃/FeVO₄/Bi₂O₃ sonocatalyst is studied in degradation of ceftriaxone sodium under ultrasonic irradiation. In addition, the influences of ultrasonic irradiation time, scavengers and sonocatalyst used times on sonocatalytic degradation of ceftriaxone sodium are examined. Under the experimental conditions of 150 min ultrasonic irradiation time, 1.00 g/L KTaO₃/FeVO₄/Bi₂O₃ addition amount and 10.00 mg/L ceftriaxone sodium concentration, the sonocatalytic degradation ratio of ceftriaxone sodium achieves 81.30%. Finally, the possible sonocatalytic degradation mechanism of ceftriaxone sodium caused by Z-scheme KTaO₃/FeVO₄/Bi₂O₃ sonocatalyst is proposed. The enhanced sonocatalytic activity may be attributed to the fact that the FeVO₄ as a special conductive channel provides a strong driving force to transfer electrons through valence state changes of iron and vanadium, which accelerates electron transfer from conduction band (CB) of Bi₂O₃ to valence band (VB) of KTaO₃. Perhaps, the KTaO₃/FeVO₄/Bi₂O₃ composite is an excellent Z-scheme sonocatalyst which can be used to effectively degrade the organic pollutants in wastewater under ultrasonic irradiation.

Synthesis of Novel Phenyl Porous Organic Polymers and Their Excellent Visible Light Photocatalytic Performance on Antibiotics

The efficient and green removal of residual antibiotics in the environment is an attractive topic. In this work, four different phenyl porous organic polymers (P-POPs) photocatalysts were successfully synthesized, and a series of techniques, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), nitrogen adsorption and desorption experimentation, and solid ultraviolet visible spectroscopy (UV-vis) were conducted to characterize the obtained P-POPs. Moreover, the photocatalytic property of P-POPs in the removal of tetracycline was studied, and the reaction conditions were optimized. Further study indicated that the P-POPs were also efficient for removing other antibiotics, such as chloramphenicol, in a high removal rate of 77%. Furthermore, the separation of the photocatalysts from the solution was easy, and the photocatalysts could be reused at least four times without a considerable loss in catalytic activity.

Development and evaluation of diffusive gradients in thin films based on nano-sized zinc oxide particles for the in situ sampling of tetracyclines in pig breeding wastewater

The pollution of antibiotics, including tetracyclines (TCs), in aquatic environments has become an issue of concern in recent years. Herein, an in situ sampling of TCs in pig breeding wastewater that utilizes the technique of diffusive gradients in thin films (DGT), based on commercial nanosized ZnO (nanoZnO) particles as the potential effective binding agent and a polyethersulfone (PES) membrane as the diffusion layer, was developed. The diffusion coefficients of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in a PES membrane at 25 °C were (1.37 ± 0.06) × 10^-6 cm² s^-1, (1.29 ± 0.05) × 10^-6 cm² s^-1 and (1.94 ± 0.07) × 10^-6 cm² s^-1, respectively. The results showed that the adsorption capacities of a gel disc containing 2.5 g L^-1 of nanoZnO particles were as high as 3.93 ± 0.20 mg disc^-1 for TC, 3.21 ± 0.20 mg disc^-1 for OTC and 4.62 ± 0.22 mg disc^-1 for CTC. Both a solution pH in the range of 5-9 and an ionic strength (as pNaCl) in the range of 1-3 had an insignificant influence on the TCs uptake by nanoZnO-DGT samplers. There was no significant influence of fulvic acid or tannic acid on the TC uptake by nanoZnO-DGT samplers at the tested mass ratios. For all spiked freshwater samples, there was no notable interference of matrices on the performance of the nanoZnO-DGT samplers, suggesting that the nanoZnO-DGT samplers yielded satisfactory results for the uptake of TCs at concentrations existing in the spiked freshwater samples. Field deployment of the nanoZnO-DGT samplers in pig breeding wastewater also exhibited excellent precision and accuracy, indicating that the nanoZnO-DGT samplers could be used as a promising method for the in situ sampling of TC antibiotics in aquatic environments.

Hierarchical magnetic petal-like Fe3O4-ZnO@g-C3N4 for removal of sulfamethoxazole, suppression of photocorrosion, by-products identification and toxicity assessment

Herein, a petal-like photocatalyst, Fe₃O₄-ZnO@g-C₃N₄ (FZG) with different g-C₃N₄ to ZnO ratios was synthesized with hierarchical structure. The FZG1 photocatalyst, having the weight ratio of 1:1 for the initial urea and Fe₃O₄-ZnO (Fe-ZnO), presented the highest sulfamethoxazole (SMX) degradation rate of 0.0351 (min^-1), which was 2.6 times higher than that of pristine ZnO. Besides the facile separation, the performance of photocatalyst was improved due to the function of iron oxide as an electron acceptor that reduced the electron/hole recombination rate. The coating of g-C₃N₄ on the Fe-ZnO surface not only acted as a protective layer for ZnO against photocorrosion, but it also enhanced the photocatalytic activity of the catalyst for SMX degradation through the heterojunction mechanism. By using the FZG1 photocatalyst, 95% SMX removal was obtained after 90 min reaction, while 47% COD and 30% TOC removal were achieved after 60 min treatment under a low energy-consuming UV lamp (10 W). Moreover, a substantial reduction in the solution toxicity was shown after the treatment, as compared with the SMX solution before treatment. The LC-HR-MS/MS analysis results showed that the concentration of most detected by-products produced after 90 min reaction by FZG1 was considerably lower than those obtained using other synthesized photocatalysts. By performing radical scavenging experiments, OH^° radical was found to be the major reactive species. The FZG1 photocatalyst also displayed excellent reusability in five cycles and the leaching of zinc and iron ions was reduced by 54% and ∼100%, respectively, after coating Fe-ZnO with g-C₃N₄.

Construction of magnetically separable NiAl LDH/Fe3O4–RGO nanocomposites with enhanced photocatalytic performance under visible light

The characterization and photocatalytic properties of magnetic NiAl LDH/Fe₃O₄–RGO composites were investigated.

Ternary semiconductor ZnxAg1−xS nanocomposites for efficient photocatalytic degradation of organophosphorus pesticides

Some approaches have been carried out for the degradation of organophosphorus pesticides using simple metal oxide nanostructures. This paper reports a comparison of the photocatalytic activity of ZnS and Ag₂S with that of ternary semiconductor Zn_0.5Ag_0.5S nanocomposites without any surfactant for the degradation of the pesticides MLT, MCP, and CPS under UV light for environmental safety.

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.

Sulfur-doped CoFe2O4 nanopowders for enhanced visible-light photocatalytic activity and magnetic properties

Magnetic recovery S-CoFe₂O₄ nanopowders showed excellent visible photocatalytic degradation of oxytetracycline and recycling performances in aqueous solution.

Fabrication of an Ag/Fe2O3/ZnO ternary composite with enhanced photocatalytic performance

A novel Ag/Fe₂O₃/ZnO ternary composite was fabricated using the chemical deposition and photochemical deposition methods.