Multi-dimensional zinc oxide (ZnO) nanoarchitectures as efficient photocatalysts: What is the fundamental factor that determines photoactivity in ZnO?

Synthesis and Mechanism of 1D ZnO Based on Alkaline Dissolution-Conversion Strategy of High Stable and Soluble ɛ-Zn(OH)2

A high soluble and stable ɛ-Zn(OH)2 precursor is synthesized at below room temperature to efficiently prepare ZnO whiskers. The experimental results indicate that the formation of ZnO whiskers is carried out mainly via two steps: the formation of ZnO seeds from ɛ-Zn(OH)2 via the in situ solid conversion, and the following growth of whiskers via dissolution-precipitation route. The decrease of temperature from 25 to 5 °C promotes the formation of ɛ-Zn(OH)2 with higher solubility and stability, which balances the conversion and dissolution rates of precursor. The Rietveld refinement, DFT calculations and MD simulations reveal that the primary reason for these characteristics is the expansion of ɛ-Zn(OH)2 lattice due to temperature, causing difficulties in the dehydration of adjacent ─OH. Simultaneously, the larger specific surface area favors the dissolution of ɛ-Zn(OH)2. Based on this precursor, well-dispersed ZnO whiskers with 9.82 µm in length, 242.38 nm in diameter, and an average aspect ratio of 41 are successfully synthesized through a SDSN-assisted hydrothermal process at 80 °C. The process has an extremely high solid content of 2.5% (mass ratio of ZnO to solution) and an overall yield of 92%, which offers a new approach for the scaled synthesis of high aspect ratio ZnO whiskers by liquid-phase method.

Biomimetic green synthesis of ZnO nanoflowers using α-amylase: from antimicrobial to toxicological evaluation

Biologically mediated synthesis of nanomaterials has emerged as an ecologically benign and biocompatible approach. Our study explores enzymatic synthesis, utilizing α-amylase to synthesize ZnO nanoflowers (ZnO-NFs). X-ray diffraction and energy-dispersive X-ray spectroscopy revealed crystal structure and elemental composition. Dynamic light scattering analysis indicates that ZnO-NFs possess a size of 101 nm. Transmission electron microscopy showed a star-shaped morphology of ZnO-NFs with petal-like structures. ZnO-NFs exhibit potent photocatalytic properties, degrading 90% eosin, 87% methylene blue, and 81% reactive red dyes under UV light, with kinetics fitting the Langmuir-Hinshelwood pseudo-first-order rate law. The impact of pH and interfering substances on dye degradation was explored. ZnO-NFs display efficient bacteriocidal activity against different Gram-positive and negative strains, antibiofilm potential (especially with P. aeruginosa), and hemocompatibility up to 600 ppm, suggesting versatile potential in healthcare and environmental remediation applications.

Photocatalytic degradation of tetracycline using a novel WO3-ZnO/AC under visible light irradiation: Optimization of effective factors by RSM-CCD

Mitigating pharmaceutical pollution in the global environment is imperative, and tetracycline (TC) is a commonly utilized antibiotic in human and veterinary medicine. The persistent existence of TC highlights the necessity of establishing efficient measures to protect water systems and the environment from detrimental contaminants. Herein, a novel rhubarb seed waste-derived activated carbon-supported photocatalyst (WO3-ZnO/RUAC) was synthesized by combining wet impregnation and ultrasonic methods. The activated carbon (AC) was obtained from rhubarb seed waste for the first time via chemical activation. The function of AC as an electron acceptor and in separating electron-hole pairs was illuminated by characterization analyses that included XRD, FTIR, XPS, SEM, TEM, PL, EIS, TPC, and UV-DRS. Using the response surface methodology-central composite design (RSM-CCD) technique, the synthesis parameters of the composite were systematically optimized. Under ideal conditions, with a TC concentration of 33 mg. L-1, pH of 4.57, irradiation time of 108 min, and catalyst dose of 0.85 g. L-1, the highest degradation efficiency of TC by this composite, achieved 96.5%, and it was reusable for five cycles. Subsequently, trapping tests and electron spin resonance (ESR) analysis were conducted, elucidating that •OH and •O2- radicals played pivotal roles in the photocatalytic degradation of TC. This research offers valuable insights into utilizing the AC-based photocatalyst to degrade pharmaceutical micropollutants effectively.

Progress in the Synthesis and Application of Transparent Conducting Film of AZO (ZnO:Al)

Due to the excellent performance and low cost of the new aluminum-doped zinc oxide (AZO) film, it is expected to replace the mature indium-doped tin oxide (ITO) film. The research status and progress of AZO transparent conductive films are summarized in this review. Moreover, the structure, optoelectronic properties, and conductive mechanism of AZO thin films are also detailed. The thin films' main preparation processes and the advantages and disadvantages of each process method are mainly discussed, and their application fields are expounded. AZO thin films with multicomponent composite structures are one of the promising development directions in transparent conductive oxide (TCO) thin films. The development of various preparation processes has promoted the production and application of thin films on a broad scale. Finally, some improvement schemes have been proposed to improve the comprehensive performance of the film. The industrialization prospects of the AZO film, as well as its great development potential in the digital world, are discussed.

Recyclable Carbon Cloth-Supported ZnO@Ag3PO4 Core-Shell Structure for Photocatalytic Degradation of Organic Dye

The extensive use of organic dyes in industry has caused serious environmental problems, and photocatalysis is a potential solution to water pollution by organic dyes. The practical application of powdery photocatalysts is usually limited by the rapid recombination of charge carriers and difficulty in recycling. In this study, recyclable carbon cloth-supported ZnO@Ag₃PO₄ composite with a core-shell structure was successfully prepared by solvothermal treatment and subsequent impregnation-deposition. The as-prepared carbon cloth-supported ZnO@Ag₃PO₄ composite showed an improved photocatalytic activity and stability for the degradation of rhodamine B (RhB), a model organic dye, under visible light irradiation. The decomposition ratio of RhB reached 87.1% after exposure to visible light for 100 min, corresponding to a reaction rate constant that was 4.8 and 15.9 times that of carbon cloth-supported Ag₃PO₄ or ZnO alone. The enhanced performance of the composite can be attributed to the effectively inhibited recombination of photoinduced electron-hole pairs by the S-scheme heterojunction. The carbon fibers further promoted the transfer of charges. Moreover, the carbon cloth-supported ZnO@Ag₃PO₄ can be easily separated from the solution and repeatedly used, demonstrating a fair recyclability and potential in practical applications.

Electrospun Polycaprolactone/ZnO Nanocomposite Membranes with High Antipathogen Activity

The spread of bacterial, fungal, and viral diseases by airborne aerosol flows poses a serious threat to human health, so the development of highly effective antibacterial, antifungal and antiviral filters to protect the respiratory system is in great demand. In this study, we developed ZnO-modified polycaprolactone nanofibers (PCL-ZnO) by treating the nanofiber surface with plasma in a gaseous mixture of Ar/CO₂/C₂H₄ followed by the deposition of ZnO nanoparticles (NPs). The structure and chemical composition of the composite fibers were characterized by SEM, TEM, EDX, FTIR, and XPS methods. We demonstrated high material stability. The mats were tested against Gram-positive and Gram-negative pathogenic bacteria and pathogenic fungi and demonstrated high antibacterial and antifungal activity.

The Influence of Al Doping on the Optical Characteristics of ZnO Nanopowders Obtained by the Low-Cost Sol-Gel Method

In this work, the influence of Al (0, 2, 4, and 6 wt.%) on the optical properties of ZnO has been briefly investigated and described. The undoped and doped samples were characterized using a UV-visible spectrophotometer and Photoluminescence (PL). The X-ray diffraction (XRD) data in our preceding study is also indexed, and materials are said to have a wurtzite-structured hexagonal phase and exhibit no impurity phases. The average crystallite sizes of the pure ZnO were found to increase, i.e., from 14.19 nm to 34.17 nm with an increase in temperature, and in the case of Al-doped ZnO, at a constant temperature, from 35.05 nm to 18.89 nm, respectively. The average crystallite size of AZO (Al-doped ZnO) decreases with increasing Al content. With the increasing temperature, increases in crystallinity and size of the pure ZnO have been observed. In the case of Al doping, with an increase in the concentration of doping the crystallite size is seen to be decreased, without any change in the temperature. Al doping improves the formation of the well-ordered crystalline structure of ZnO up to a certain limit of doping. The absorbance spectra were used to determine the optical band gap of the samples. The optical photoluminescence (PL) spectra of both ZnO and AZO nanopowder are obviously influenced by the increasing temperature and Al doping content, respectively. Different optical properties of ZnO and AZO were observed for different contents of Al in ZnO. The band gap of AZO nanopowder with different concentrations has been seen to be lower than that of undoped ZnO (3.10 eV), suggesting broad application potential. Also, the optical properties of ZnO were tailored by Al doping in the near visible region, suggesting various potential uses.

Comparative Study of SnO2 and ZnO Semiconductor Nanoparticles (Synthesized Using Randia echinocarpa) in the Photocatalytic Degradation of Organic Dyes

Symmetry in nanomaterials is essential to know the behavior of their properties. In the present research, the photocatalytic properties of SnO2 and ZnO nanoparticles were compared for the degradation of the cationic dyes Methylene Blue (MB) and Rhodamine B (RB). The nanoparticles were obtained through a green synthesis process assisted by Randia echinocarpa extracts; they were then analyzed through Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) to characterize their structure. Transmission electron microscopy (TEM) was used to identify the morphology and disclose nanoparticle size, and the optical properties were studied through Ultraviolet–visible spectroscopy (UV–Vis). The results show that the synthesized SnO2 and ZnO nanomaterials have quasispherical morphologies with average sizes of 8–12 and 4–6 nm, cassiterite and wurtzite crystal phases, and band gap values of 3.5 and 3.8 eV, respectively. The photocatalytic activity yielded 100% degradation of the MB and RB dyes in 210 and 150 min, respectively. ZnO performed higher photocatalytic degradation of the cationic dyes than SnO2 due to a higher content of Randia echinocarpa extracts remaining after the green synthesis process.

Dimensional Optimization for ZnO-Based Mechano-ATRP with Extraordinary Activity

Various piezoelectric nanomaterials were utilized in ultrasound-mediated atom transfer radical polymerization (ATRP), owing to their outstanding piezoelectric effect. However, the relationship between the morphology of those piezocatalysts and polymerization has not been clearly established. Herein, we employed different piezoelectric zinc oxide (ZnO) nanomaterials to achieve novel mechano-induced ATRP (mechano-ATRP). Based on the synergistic effect of piezoelectric properties and specific surface area, the catalytic activity of 1D ZnO nanorods (1D-ZnO NRs) with increased aspect ratio outperformed that of 0D ZnO nanoparticles (0D-ZnO NPs). Compared to the conventional ATRP system, this system exhibited extraordinary activity toward the less activated monomer acrylonitrile (67% conversion after 6 h), with a narrow molecular weight distribution (polydispersity index ∼ 1.19). Furthermore, implications of ZnO loading, copper salt amount, degree of polymerization, monomer, and solvent were also studied for the highly efficient mechano-ATRP.

Enhanced photocatalytic activity of Fe2O3@ZnO decorated CQD for inactivation of Escherichia coli under visible light irradiation

The present study, magnetically separable Fe₂O₃@ZnO/CQD nanocomposite was successfully prepared via hydrothermal process and characterized with SEM-EDX, XRD, FTIR, VSM and DRS analysis. The effect of operational parameters includes photocatalyst dosage, photocatalyst type, CQD content and Escherichia coli (E. coli) concentration were evaluated on the E. coli inactivation. The disinfecting ability of nanocomposite components was obtained as Fe₂O₃@ZnO/CQD> Fe₂O₃@ZnO> ZnO> Fe₂O₃> CQD which shows a synergetic effect among different components. The highest E. coli inactivation rate (K_max=0.7606 min^-1) was obtained at photocatalyst dosage of 0.2 g/L and 15% CQD content. The MIC and MBC values value for E. coli were determined 0.1172 mg/mL and 0.4948 respectively that the results tests proved the antibacterial functions of the Fe₂O₃@ZnO/CQD. Nanocomposite showed the high reusability after 4 consecutive cycles, K_max decreased from 0.7606 min^-1 to 0.6181 min^-1. Quenching experiments showed ^•OH and h⁺ are the main reactive oxygen species involved in the E. coli inactivation.

Adsorption-enhanced photocatalytic property of Ag-doped biochar/g-C3N4/TiO2 composite by incorporating cotton-based biochar

In this study, the biochar obtained from waste cotton fibers was introduced into the Ag-doped g-C3N4/TiO2 hybrid composite through a facile one-step hydrothermal process. The morphology, elemental composition, crystal structure, microstructure, specific surface area, chemical bonding state, energy band structure, and separation efficiency of photoinduced charge carriers of the resultant composite were examined using scanning electron microscope, energy dispersive X-ray spectrometer, X-ray diffractometer, transmission electron microscope, surface area analyzer, X-ray photoelectron spectroscope, Ultraviolet-visible spectrophotometer, ultraviolet photoelectron spectroscope, and photoluminescence spectroscope. The adsorption isotherms, kinetics and thermodynamics of the biochar, Ag-doped g-C3N4/TiO2 and Ag-doped biochar/g-C3N4/TiO2 were evaluated using the model methyl orange dye. The photoacatalytic degradation of the model pollutants including methyl orange, methylene blue, congo red, and tetracycline hydrochloride and the photocatalytic reduction of Cr(VI) ions were also assessed under visible light. Experimental results indicated that the photocatalytic property of the Ag-doped biochar/g-C3N4/TiO2 was significantly enhanced through the adsorption enhancement compared with the Ag-doped g-C3N4/TiO2. This was due to the uniform doping of multi-scale porous biochar with g-C3N4 nanosheet, Ag and TiO2 nanoparticles. The adsorptive enhancement induced by the biochar resulted in the narrowed band gap, suitable electronic energy band structure, and fast separation of photoinduced charge carriers of the Ag-doped biochar/g-C3N4/TiO2, which was probably due to the coexistence of multi-valence Ti+4/+3 and Ag0/+1 species and oxygen-containing groups of biochar. The major reactive species of the Ag-doped biochar/g-C3N4/TiO2 were 1O2 and h+. The MO dye adsorption onto the Ag-doped biochar/g-C3N4/TiO2 followed the Langmuir isotherm model, pseudo-first-order and pseudo-second-order kinetic models, and the adsorption process was an endothermic reaction with entropy reduction effects. As such, the Ag-doped biochar/g-C3N4/TiO2 exhibited a promising application for the treatment of wastewater containing multi-pollutants especially organic dyes and heavy metal ions.

State-of-the-art biosynthesis of tin oxide nanoparticles by chemical precipitation method towards photocatalytic application

Tin oxide (SnO₂) with versatile properties is of substantial standing for practical application, and improved features of the material are demonstrated in the current issue through the integration of nanotechnology with bio-resources leading to what is termed as biosynthesis of SnO₂ nanoparticles (NPs). This review reveals the recent advances in biosynthesis of SnO₂ NPs by chemical precipitation method focused on distinct methodologies, characterization, and reaction mechanism along with a photocatalytic application for dye degradation. According to available literature reviews, numerous bio-based precursors selectively extracted from biological substrates have effectively been applied as capping or reducing agents to achieve the metal oxide NPs. The major precursor obtained from the aqueous extract of root barks of Catunaregam spinosa is found to be 7-hydroxy-6-methoxy-2H-chromen-2-one that has been proposed as a model compound for the reduction of metal ions into nanoparticles due to having highly active functional groups, being abundant in plants (67.475 wt%), easy to extract, and eco benign. In addition, the photocatalytic activity of SnO₂ NPs for the degradation of organic dyes, pharmaceuticals, and agricultural contaminants has been discussed in the context of a promising bio-reduction mechanism of the synthesis. The final properties are supposed to depend exclusively upon a number of factors, e.g., particle size (< 50 nm), bandgap (< 3.6 eV), crystal defects, and catalysts dosage. With this contribution, it has been perceived not only to provide an overview of recent advances in the biosynthesis of SnO₂ NPs but also to indicate the main issues in need aiming to show vision towards innovative outcomes.

Visible light-assisted degradation of 4-nitrophenol and methylene blue using low energy carbon ion-implanted ZnO nanorod arrays: Effect on mechanistic insights and stability

The present investigation demonstrates an enhancement of the visible photocatalytic activities by C ion implantation in ZnO nanorod arrays (NRAs). Vertically aligned ZnO NRAs were prepared by seed layer assisted solution-phase growth and implanted with 70 keV carbon ions at various fluencies: 1E15, 5E15, 1E16, and 3E16 ions/cm². X-ray diffraction and FESEM results revealed the crystalline 1D ZnO NRAs having a length of ∼3 μm with a diameter in the range of 150-200 nm. C implantation induces the absorption towards the visible region and a substantial decrease in the optical bandgap energy from 3.2 eV to 2.43 eV. The photocatalytic activities (PC) of C ion-implanted ZnO NRAs were investigated through the degradation of 4-Nitrophenol (4-NP) and methylene blue dye (MB) under ambient visible light irradiation. The degradation efficiency of C ion-implanted ZnO NRAs increases compared to the pristine ZnO NRAs from 60.12% to 93.7% and 48.6 to 97.5% for MB and 4-NP, respectively. The synergistic effects of low energy carbon ion-induced bulk and surface interface electronic states facilitate a narrow band of visible light absorption and efficient charge separation to increase the visible-light-driven photocatalytic performance of ZnO NRAs.

Visible-light-driven photocatalytic inactivation of S. aureus in aqueous environment by hydrophilic zinc oxide (ZnO) nanoparticles based on the interfacial electron transfer in S. aureus/ZnO composites

Waterborne diseases caused by pathogenic microorganisms pose severe threats to human health. ZnO nanoparticles (NPs) hold great potentials as an effective, economical and eco-friendly method for water disinfection, but the exact antimicrobial mechanism of ZnO NPs under visible-light illumination is still not clear. Herein, we investigate the visible-light-driven photocatalytic inactivation mechanism of amino-functionalized hydrophilic ZnO (AH-ZnO) NPs against Staphylococcus aureus (S. aureus) in aqueous environment from the perspective of electron transfer theory. The results show that the antibacterial effects of AH-ZnO NPs are dependent on the AH-ZnO NPs concentration and treatment time. The bulk ORP value and released Zn²⁺ concentration in AH-ZnO NPs solutions increase with AH-ZnO NPs concentration. The SEM and intracellular protein leakage results indicate that AH-ZnO NPs can adhere to S. aureus surface without causing obvious cell membrane disruption. The photoluminescence (PL) intensity and fluorescence lifetime of AH-ZnO NPs are remarkedly decreased after adding S. aureus, which confirms the electron transfer from S. aureus to AH-ZnO NPs. Moreover, the ΔPL intensity is closely correlated with the inactivation efficiency, demonstrating that the interfacial electron transfer in S. aureus/AH-ZnO NPs composites contributes to the antibacterial activity, which is speculated to disrupt the normal respiratory electron transfer chain of S. aureus, thereby causing intracellular ROS generation, cell membrane depolarization and eventually apoptosis-like death.

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.

Morphology effect on zinc oxide quantum photoinitiators for radical polymerization

Semiconductor nanocrystal based photoinitiators, quantum PIs, are a viable alternative to organic photoinitiators demonstrating unique advantages, including a broad and tunable excitation window, limited migration, and more. Aiming towards efficient quantum PIs with tunable properties, a deeper understanding of the relationships between the nanoparticle properties and their efficiency is required. Herein, we studied the morphological effect on ZnO nanocrystals functioning as photoinitiators in both water-based and solvent-free formulations by comparing rod and pyramidal shaped particles of similar volumes and nearly identical surface area. Superior polymerization performances are measured for the nanorods. Photocatalytic characterization including oxygen consumption and reactive oxygen species formation as well as dyes reduction and oxidation, also showed enhanced activities for the nanorods. The different performances were attributed to the anisotropic nanorod morphology which is beneficial for charge separation as well as to the presence of a reactive [0001] facet in the nanorods, which is known to increase the adsorption of molecular oxygen and anionic molecules, thus affecting the catalytic activity. These observations, along with the higher photoinitiation efficiency of the ZnO nanorods, bring them closer to functionality as photoinitiators in numerous photopolymerization applications.

Recent Advances in Zinc Oxide Nanostructures with Antimicrobial Activities

This article reviews the recent developments in the synthesis, antibacterial activity, and visible-light photocatalytic bacterial inactivation of nano-zinc oxide. Polycrystalline wurtzite ZnO nanostructures with a hexagonal lattice having different shapes can be synthesized by means of vapor-, liquid-, and solid-phase processing techniques. Among these, ZnO hierarchical nanostructures prepared from the liquid phase route are commonly used for antimicrobial activity. In particular, plant extract-mediated biosynthesis is a single step process for preparing nano-ZnO without using surfactants and toxic chemicals. The phytochemical molecules of natural plant extracts are attractive agents for reducing and stabilizing zinc ions of zinc salt precursors to form green ZnO nanostructures. The peel extracts of certain citrus fruits like grapefruits, lemons and oranges, acting as excellent chelating agents for zinc ions. Furthermore, phytochemicals of the plant extracts capped on ZnO nanomaterials are very effective for killing various bacterial strains, leading to low minimum inhibitory concentration (MIC) values. Bioactive phytocompounds from green ZnO also inhibit hemolysis of Staphylococcus aureus infected red blood cells and inflammatory activity of mammalian immune system. In general, three mechanisms have been adopted to explain bactericidal activity of ZnO nanomaterials, including direct contact killing, reactive oxygen species (ROS) production, and released zinc ion inactivation. These toxic effects lead to the destruction of bacterial membrane, denaturation of enzyme, inhibition of cellular respiration and deoxyribonucleic acid replication, causing leakage of the cytoplasmic content and eventual cell death. Meanwhile, antimicrobial activity of doped and modified ZnO nanomaterials under visible light can be attributed to photogeneration of ROS on their surfaces. Thus particular attention is paid to the design and synthesis of visible light-activated ZnO photocatalysts with antibacterial properties.

Eco-friendly synthesis and photocatalytic application of flowers-like ZnO structures using Arabic and Karaya Gums

Flowers-like ZnO structures were synthesized using Arabic Gum (AGZnO) or Karaya Gum (KGZnO). The AGZnO and KGZnO were characterized by X-ray diffractometry, Fourier Transformed Infrared, Scanning Electron Microscopy, Photoluminescence, nitrogen adsorption/desorption and diffuse reflectance techniques. The materials were tested in the discoloration of Methylene Blue (MB) dye under visible light and scavenger studies were also performed. The toxicity of the MB irradiated was investigated in bioassays with Artemia salina. The structural characterization demonstrated the formation of hexagonal ZnO. All samples presented flower-like morphology with presence of mesopores identified by BET method. The optical properties indicated band gap of 2.99 (AGZnO) and 2.76 eV (KGZnO), and emission in violet, blue and green emissions also were observed. The KGZnO demonstrated better photocatalytic performance than the AGZnO, and scavenger studies indicated that OH radicals are the main species involved in the degradation of the pollutant model. The photodiscoloration of MB solution did not demonstrate toxicity. Therefore, KGZnO is a promising material for photocatalysis application.

Anticorrosion Coated Stainless Steel as Durable Support for C-N-TiO2 Photo Catalyst Layer

The development of durable photocatalytic supports resistant in harsh environment has become challenging in advanced oxidation processes (AOPs) focusing on water and wastewater remediation. In this study, stainless steel (SS), SS/Ti (N,O) and SS/Cr-N/Cr (N,O) anticorrosion layers on SS meshes were dip-coated with sol gel synthesised C-N-TiO₂ photo catalysts pyrolysed at 350 °C for 105 min, using a heating rate of 50 °C/min under N₂ gas. The supported C-N-TiO₂ films were characterised by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that C-N-TiO₂ was successfully deposited on anticorrosion coated SS supports and had different morphologies. The amorphous C and TiO₂ were predominant in C-N-TiO₂ over anatase and rutile phases on the surface of SS and anticorrosion supports. The C-N-TiO₂ coated films showed enhanced photocatalytic activity for the decolouration of O.II dye under both solar and UV radiations. The fabricated C-N-TiO₂ films showed significant antibacterial activities in the dark as well as in visible light. Herein, we demonstrate that SS/Ti(N,O) and SS/Cr-N/Cr(N,O) anticorrosion coatings are adequate photocatalytic and corrosion resistant supports. The C-N-TiO₂ photo catalytic coatings can be used for water and wastewater decontamination of pollutants and microbes.

Progress in Graphene/Metal Oxide Composite Photocatalysts for Degradation of Organic Pollutants

The sewage discharge of industrial wastewater seriously pollutes the water source and rivers, which is very harmful to the health of humans and wildlife. Among those methods for treating wastewater, photocatalysis is a sustainable and environmental-friendly technique for removing the organic pollutants with no secondary pollution. As a popular photocatalyst, graphene/metal oxide nanocomposites have been widely reported in the photocatalysis field. In this review, the recent progress of graphene/metal oxide composites including binary and ternary composites is summarized in detail. The synthesis, microstructure design, and application performance of graphene/TiO2, graphene/ZnO, graphene/SnO2, graphene/WO3, graphene/Fe2O3, and graphene/Cu2O composites are introduced firstly. Then, the synthesis, the selection of components, and the performance of various ternary composites are summarized specifically, including graphene/TiO2-, graphene/ZnO-, graphene/SnO2-, graphene/Cu2O-, graphene/FexOy-, and graphene/Bi-containing ternary composites. At last, the possible research directions of graphene/metal oxide nanocomposites are put forward. The main purpose is to provide a theoretical guidance for designing high-performance graphene/metal oxide photocatalysts for wastewater treatment.

Visible-light driven degradation of tetracycline hydrochloride and 2,4-dichlorophenol by film-like N-carbon@N-ZnO catalyst with three-dimensional interconnected nanofibrous structure

The emergence of more and more persistent organic molecules as contaminants in water simulates research towards the development of more advanced technologies, among which photocatalysis is a feasible choice. However, it is still challenging to design a photocatalyst that fulfills all the requirements for industrial application, i.e., active under visible-light irradiation, shape with handy convenience, highly uniform distribution of active sites, substrate with excellent electronic properties, etc. In this study, we report an attempt to solve these issues at once by designing a film-like photocatalyst with uniform distribution of nitrogen-doped ZnO nanoparticles along nitrogen-doped carbon ultrafine nanofibers with three-dimensional interconnected structure. Under visible-light irradiation, the product exhibited remarkable reactivity for the degradation of two model pollutants tetracycline hydrochloride and 2,4-dichlorophenol within 100 min. The cyclic experiments demonstrated only a slight loss (ca. 5 %) of reactivity after five consecutive photocatalytic reactions. We also investigated the detailed relationship between the structural features and the superior properties of this product, as well as the degradation mechanisms. The convenient shape of the product with excellent performances for the treatment of real polluted water increases its suitability for larger scale application. Our work provides a rational design of photocatalysts for environmental remediation.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphoslogies

Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.

Impacts of morphological-controlled ZnO nanoarchitectures on aerobic microbial communities during real wastewater treatment in an aerobic-photocatalytic system

This study aimed to evaluate the impacts of morphological-controlled ZnO nanoarchitectures on aerobic microbial communities during real wastewater treatment in an aerobic-photocatalytic system. Results showed that the antibacterial properties of ZnO nanoarchitectures were significantly more overwhelming than their photocatalytic properties. The inhibition of microbial activities in activated sludge by ZnO nanoarchitectures entailed an adverse effect on wastewater treatment efficiency. Subsequently, the 16S sequencing analysis were conducted to examine the impacts of ZnO nanoarchitectures on aerobic microbial communities, and found the significantly lower microbial diversity and species richness in activated sludge treated with 1D-ZnO nanorods as compared to other ZnO nanoarchitectures. Additionally, 1D-ZnO nanorods reduced the highest proportion of Proteobacteria phylum in activated sludge due to its higher proportion of active polar surfaces that facilitates Zn²⁺ ions dissolution. Pearson correlation coefficients showed that the experimental data obtained from COD removal efficiency and bacterial log reduction were statistically significant (p-value < 0.05), and presented a positive correlation with the concentration of Zn²⁺ ions. Finally, a non-parametric analysis of Friedman test and post-hoc analysis confirmed that the concentration of Zn²⁺ ions being released from ZnO nanoarchitectures is the main contributing factor for both the reduction in COD removal efficiency and bacterial log reduction.