Effect of induced defects on the properties of ZnO nanocrystals: surfactant role and spectroscopic analysis

Comparative evaluation of α-Bi2O3/CoFe2O4 and ZnO/CoFe2O4 heterojunction nanocomposites for microwave induced catalytic degradation of tetracycline

Two microwave (MW) responsive heterojunction nanocomposite catalysts, i.e., α-Bi2O3/CoFe2O4 (BO/CFO) and ZnO/CoFe2O4 (ZO/CFO), with weight% ratio of 70/30, 50/50, 30/70 were synthesized by sequential thermal decomposition and co-precipitation methods, and used for the degradation of tetracycline (TC) under MW irradiation. The formation of desired catalysts was confirmed through the characterization results of XRD, FT-IR, SEM, VSM, UV-DRS, XPS, BET, etc. Using batch MW experiments, the catalyst dose, pH, initial TC concentration, reaction temperature, and MW power were optimized for TC removal. Under the following reaction conditions: catalyst dose ∼1 g/L, initial TC concentration ∼1 mg/L, temperature ∼90 °C, MW ∼450 W, BO/CFO, and ZO/CFO showed ∼97.55% and 88.23% TC degradation, respectively, after 5 min. The difference in the catalytic response against TC degradation indicated the difference in reflective loss (RL) between these two catalysts. The presence of other competitive anions has affected the removal efficiency of TC due to the scavenging effect. The radical trapping study revealed the significant contribution of TC degradation by hydroxyl radicals in the case of ZO/CFO, whereas for BO/CFO, superoxide (●O2-) and hydroxyl radicals (●OH) both played influential roles. The Z-scheme heterojunction of BO/CFO allowed the formation of ●O2- but the same was inhibited in type-II heterojunction of ZO/CFO due to the valance band position. The dielectric loss, magnetic loss, interfacial polarization, and high electrical conductivity, 'hotspots' were produced over the catalyst surface alongside electron-hole separation at heterojunctions, which were responsible for the generation of reactive oxygen species. In addition, Co3+/Co2+ and Fe3+/Fe2+ redox cycles have promoted ●O2- and sulfate radical production during persulfate application. Among the two MW responsive catalysts, BO/CFO could be a potential material for rapidly destroying emerging organic pollutants from wastewater without applying other oxidative chemicals under MW irradiation.

Sunflower Pollen-Morphology Mimicked Spiky Zinc Nanomotors as a Photosensitizer for Killing Bacteria and Cancer Cells

Photosensitizing agents have received increased attention from the medical community, owing to their higher photothermal efficiency, induction of hyperthermia, and sustained delivery of bioactive molecules to their targets. Micro/nanorobots can be used as ideal photosensitizing agents by utilizing various physical stimuli for the targeted killing of pathogens (e.g., bacteria) and cancer cells. Herein, we report sunflower-pollen-inspired spiky zinc oxide (s-ZnO)-based nanorobots that effectively kill bacteria and cancer cells under near-infrared (NIR) light irradiation. The as-fabricated s-ZnO was modified with a catechol-containing photothermal agent, polydopamine (PDA), to improve its NIR-responsive properties, followed by the addition of antimicrobial (e.g., tetracycline/TCN) and anticancer (e.g., doxorubicin/DOX) drugs. The fabricated s-ZnO/PDA@Drug nanobots exhibited unique locomotory behavior with an average speed ranging from 13 to 14 μm/s under 2.0 W/cm2 NIR light irradiation. Moreover, the s-ZnO/PDA@TCN nanobots exhibited superior antibacterial activity against E. coli and S. epidermidis under NIR irradiation. The s-ZnO/PDA@DOX nanobots also displayed sufficient reactive oxygen species (ROS) amplification in B16F10 melanoma cells and induced apoptosis under NIR light, indicating their therapeutic efficacy. We hope the sunflower pollen-inspired s-ZnO nanorobots have tremendous potential in biomedical engineering from the phototherapy perspective, with the hope to reduce pathogen infections.

Debromination of novel brominated flame retardants using Zn-based additives: A viable thermochemical approach in the mitigation of toxic effects during e-waste recycling

Brominated flame retardants (BFRs) are bromine-bearing additives added to the polymeric fraction in various applications to impede fire ignition. The Stockholm Convention and various other legislations abolished legacy BFRs usage and hence, the so-called novel BFRs (NBFRs) were introduced into the market. Recent studies spotlighted their existence in household dust, aquifers and aquatic/aerial species. Co-pyrolysis of BFRs with metal oxides has emerged as a potent chemical recycling approach that produces a bromine-free stream of hydrocarbon. Herein, we investigate the debromination of two prominent two NBFRs; namely tetrabromobisphenol A 2,3-dibromopropyl ether (TD) and tetrabromobisphenol A diallyl ether (TAE) through their co-pyrolysis with zinc oxide (ZnO) and franklinite (ZnFe2O4). Most of the zinc content in electrical arc furnace dust (EAFD) exists in the form of these two metal oxides. Conversion of these metal oxides into their respective bromides could also assist in the selective extraction of the valuable zinc content in EAFD. The debromination potential of both oxides was unveiled via a multitude of characterization studies to analyze products (char, gas and condensates). The thermogravimetric analysis suggested a pyrolytic run up to 500 °C and the TAE treatment with ZnO produced only a trivial amount of brominated compounds (relative area, 0.83%). Phenol was the sole common compound in condensable products; potentially formed by the β-scission debromination reaction from the parental molecular skeleton. Inorganic compounds and methane were the major constituents in the gaseous products. The pyrochar analyses confirmed the presence of metal bromides retained in the residue, averting the bromine release into the atmosphere. The ion chromatography analysis portrayed <8% of HBr gas release into the atmosphere upon pyrolysis with ZnO. The ZnO dominance herein envisaged further probes into other spinel ferrites in combating brominated polymers.

Investigating the effect of acidic and basic precipitation on the antibacterial activity of ZnO nanoparticles against Gram-negative and Gram-positive bacteria

In the present work, acidic (direct) and basic precipitation (indirect) methods were used to demonstrate the influence of the mode of precipitation on the structural properties of ZnO nanoparticles (NPs). Four samples of ZnO nanoparticles were prepared, two samples via each mode of precipitation. DZOa and IZOa were the aged samples prepared via acidic and basic precipitation methods, and DZOwa and IZOwa were processed without aging. Both precipitation processes were carried out without using any surfactant reagents. Zinc hydroxide precipitate, which was formed during the basic precipitation method, could be critical in deciding the properties of ZnO NPs, unlike zinc hydroxide formed during acidic precipitation. Aging of zinc hydroxide, synthesised by basic precipitation method for 48 hours was found to be an added advantage in controlling the properties of ZnO NPs. The influence of the mode of precipitation on the structural properties and antibacterial activity of ZnO NPs against Gram-positive and Gram-negative bacterial strains was tested. The antibacterial activity of all four ZnO NPs was analysed via zone of inhibition measurements at a concentration dose of 200 μg ml-1. IZOa nanoparticles prepared using the basic precipitation method showed a higher antibacterial activity against three Gram-negative and one Gram-positive strains, namely, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. DZOa nanoparticles synthesized through acidic precipitation showed relatively high antibacterial activity against Salmonella typhimurium, a Gram-negative strain. ZnO NPs prepared without aging, IZOwa and DZOwa, showed a higher antibacterial activity against E. coli and Bacillus sp. strains, respectively. All ZnO NPs were characterized via UV-visible, FTIR, XRD, and HRSEM techniques.

In situ fabrication of lanthanum-doped nickel oxide nanostructures using sol-gel for the degradation of rhodamine B

Nanoscale science represents a thriving field of research for environmental applications within materials science. This study focuses on the fabrication of pure and La-doped nickel oxide (NiO) nanostructures with varying concentrations (1.0, 2.0, 3.0, and 4.0 wt%) of lanthanum using a facile sol-gel technique. This study explores the structural, morphological, chemical composition, and optical characteristics of the resulting pure and La-doped NiO nanostructures. Techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, UV-visible spectroscopy, and photoluminescence (PL) spectroscopy were used for material analysis. The observed trend in the energy band gap (Eg) values demonstrates a continuous decrease up to a La-doping concentration of 3 wt% in NiO. However, after this concentration (at 4.0 wt%), there is a noticeable increase in the energy band gap. At lower La-doping concentrations (up to 3 wt%), the incorporation of La ions into the NiO lattice may result in the formation of defects and oxygen vacancies. The presence of these imperfections may lead to new energy levels into the band gap, resulting in partial filling and a subsequent reduction in the band gap. Beyond a specific doping concentration (e.g., 3 wt%), excess La atoms may aggregate or cluster inside the NiO lattice. This agglomeration may cause structural distortions, strain, and disturbances in the crystal lattice, resulting in an increase in the band gap. The 3 wt% La-doped NiO sample demonstrated a notable 84% degradation efficiency of the synthesized nanomaterials coupled with its inherent stability, highlighting its dual attributes of effective pollutant removal and sustained performance. Furthermore, the cyclic stability of the optimized nanostructure is anticipated to be ∼77.42% after six cycles, suggesting promising future applications in photocatalysis.

ZnO/black phosphorus/C3N4 composite: An effective photocatalyst for Cr (VI) reduction and degradation of rhodamine B

The utilization of photocatalysts offers a promising approach for the removal of Cr (VI) and rhodamine dyes. Through the generation of reactive species and subsequent degradation reactions, photocatalysis provides an efficient and environmentally friendly method for the remediation of wastewater. In this study, we have synthesized an n-p-n heterojunction of carbon nitride (C3N4), zinc oxide (ZnO), and black phosphorus (BP) through the sonication-stirring method. The photocatalytic ability of this composite was examined for the decomposition rhodamine B (RhB) and detoxification of hexavalent chromium ion (up to 97% during 80 min) under Xenon irradiation. The results of trapper experiments indicated that the active species were hydroxyl radical (˙OH), electron (e-), and superoxide anion radical (˙O2-). Based on the obtained potential of the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbital (HOMO) for the mentioned semiconductors, through Mutt-Schottky results, the double Z-scheme mechanism was proposed for the studied process. The electrochemical impedance spectroscopy data exhibited good charge transfer for the evaluated composite versus the pure compounds. The impressive separation of holes and electrons along with the low recombination were confirmed by the responses of photocurrent and quenching the photoluminescence (pl) intensity for the composite, respectively. The current density of the composite recorded 66.6%, 87.3%, and 92% higher than those of BP, C3N4, and ZnO, indicating an excellent electron-hole separation for the ternary composite compared to the pure semiconductors. Diffuse reflectance spectra (DRS) data revealed 2.9, 3.17, 1.15, and 2.63 eV as the band gap values for C3N4, ZnO, BP, and composite. The rate constant of the new composite to remove RhB and reduce hexavalent chromium were about 4.79 and 2.64 times higher than that of C3N4, respectively.

Effect of P2O5 Content on Luminescence of Reduced Graphene-Oxide-Doped ZnO-P2O5 Nano-Structured Films Prepared via the Sol-Gel Method

A convenient and low-cost sol-gel approach for the one-step synthesis of ZnO-P2O5-rGO nanostructures with tuned bandgap and fluorescence was investigated. The obtained hybrid nanostructures exploit the properties of zinc oxide, graphene oxide and phosphorous oxide as promising candidates for a wide range of optoelectronic applications. A predominant amorphous structure, ZnO-P2O5-rGO, containing ZnO nanorods was evidenced by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The estimated size of the ZnO nanorods in nanostructures with P2O5 was noticed to decrease when the P2O5/ZnO ratio was increased. The presence of ZnO, P2O5 and rGO was confirmed by Fourier-transform infrared spectroscopy (FTIR) and Raman investigation. P2O5 was noticed to tune the bandgap and the fluorescence emissions of the nanostructured films, as estimated by UV-Vis-NIR and fluorescence spectroscopy, respectively. The electrical measurements performed at room temperature showed that the main influence on the film's resistivity does not come from the 1% rGO doping but from the P2O5/ZnO ratio. It was found that a 10/90 molar ratio of P2O5/ZnO decreases the resistivity almost seven-fold compared with rGO-doped ZnO films.

Recent progress on plant extract-mediated biosynthesis of ZnO-based nanocatalysts for environmental remediation: Challenges and future outlooks

The plant extract mediated green synthesis of nanomaterials has attracts enormous interest due to its cost-effectiveness, greener, and environmentally friendly. It is also considered as an alternative and facile method in which the phytochemicals can be used as a natural capping and reducing agents and helped to produce nanomaterials with high surface area, different sizes, and shapes. One of the materials fabricated using green methods is zinc oxide (ZnO) semiconductor due to its enormous applications in different field areas. In this review, an overview of recent progress on green synthesized ZnO-based catalysts and various modification methods for the purpose of enhancing the catalytic activity of ZnO and the corresponding structural-activity and interactions towards the removal of pollutants are highlighted. Particularly, the plant extract mediated ZnO-based photocatalysts application for the removal of pollutants via photocatalytic degradation, reduction reaction, and adsorption mechanism are demonstrated. Besides, the opportunities, challenges, and future outlooks of ZnO-based materials for environmental remediation with green and sustainable methods are also included. We believe that this review is a timely and comprehensive review on the recent progress related to plant extract mediated ZnO-based nanocatalysts synthesis and applications for environmental remediation.

Heterostructure charge transfer dynamics on self-assembled ZnO on electronically different single-walled carbon nanotubes

The charge transfer kinetics of the catalyst particles play a key role in advanced oxidation processes (AOP) for the complete destruction of recalcitrant and persistent contaminants in water. Here, a significant improvement in the photocatalytic performance is observed in the Single-Walled Carbon Nanotube (SWCNT)-ZnO heterostructure photocatalyst. The charge transfer dynamics and factors affecting AOP are studied using ZnO nanoparticles self-assembled onto three electronically different SWCNTs (metallic, semiconducting, and pristine) via the precipitation method, introducing a heterojunction interface. The creation of the SWCNT/ZnO heterostructure interface improves charge transfer and separation, resulting in a charge carrier lifetime of 7.37 ns. Also, surface area, pore size, and pore volumes are increased by 4.2 times compared to those of ZnO. The nanoparticles-coated face-mask fabric used as the floating photocatalyst exhibited high stability and recyclability with 99% RhB degradation efficiency under natural sunlight and 94% under UV light after the 5th cycle. The surface and crystal defects-oxygen or zinc defects/interstitials open new reaction active sites that assist in charge carrier transfer and act as pollutant absorption and interaction sites for enhanced performance. The ideal band edge positions of the valence band and conduction band favor the generation of H2O/OH•, OH·/OH, and O2/HO2• reactive oxygen species. OH• radicals are found to play a vital role in this AOP by using ethanol as an OH• scavenger.

Effect of Na and Al doping on ZnO nanoparticles for potential application in sunscreens

This study investigated the environment-friendly production and characterization of zinc oxide nanoparticles (ZnO NPs) doped with sodium (Na) and aluminum (Al) metals to decrease the photocatalytic activity of ZnO for use in sunscreen. The metal-doped zinc oxide (ZnO) materials were prepared by the microwave method using extracts of Averrhoa carambola, also known as star fruit, as a reducing agent. The effects of metal-ion doping on the crystal structure, morphology, and optical characteristics of ZnO were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), and ultraviolet-visible (UV-Vis) spectroscopy. The sun protection factor (SPF) of the sunscreen formulations containing undoped ZnO, Na-doped ZnO (Na/ZnO), and Al-doped ZnO (Al/ZnO) NPs were found to be 10.10, 25.10, and 43.08, respectively. Therefore, Na/ZnO and Al/ZnO showed increased SPF. Additionally, the prepared nanomaterials and sunscreens were effective against Gram-positive and Gram-negative bacteria and showed antioxidant activities. The methylene blue (MB) degradation was used to evaluate the photocatalytic activities of the undoped ZnO, Na/ZnO, and Al/ZnO NPs, which were found to be 66%, 46%, and 38%, respectively. Therefore, due to the structural defects of ZnO NPs, their photocatalytic activity was decreased with Na- and Al- doping. Additionally, Al/ZnO is an ideal candidate as an ingredient in sunscreens.

ZnO Tetrapods for Label-Free Optical Biosensing: Physicochemical Characterization and Functionalization Strategies

In this study, we fabricated three different ZnO tetrapodal nanostructures (ZnO-Ts) by a combustion process and studied their physicochemical properties by different techniques to evaluate their potentiality for label-free biosensing purposes. Then, we explored the chemical reactivity of ZnO-Ts by quantifying the available functional hydroxyl groups (-OH) on the transducer surface necessary for biosensor development. The best ZnO-T sample was chemically modified and bioconjugated with biotin as a model bioprobe by a multi-step procedure based on silanization and carbodiimide chemistry. The results demonstrated that the ZnO-Ts could be easily and efficiently biomodified, and sensing experiments based on the streptavidin target detection confirmed these structures' suitability for biosensing applications.

Induced defect and ZnO nano-flower formation by N, N, dimethylformamide solvent for natural sunlight responsive floating photocatalytic advanced oxidation process

The increasing disposal of dyes and face-mask propel to hunt for a solution to fight water pollution while assisting sustainability. This research overcomes the key challenges associated with implementing photocatalytic water treatment by using natural sunlight active photocatalyst, changing slurry system, eliminating the use of external triggering sources, and reusing face-mask fabric coated with ZnO to act as a floating photocatalyst. Unique morphological structures-cauliflower, hydrangea, and petals-likes are obtained with the variation in synthesis medium (Diethylene glycol (DEG), N, N-dimethyl formamide (DMF), H₂O) and methods (precipitation, solvothermal) which are found to be dependent on the solvent properties. With the use of DMF having a higher dielectric constant and formation of dimethyl amine via hydrolysis, it influences in forming petals and flower-like morphologies, unlike DEG solvent. The ZnO-coated face-mask fabric is used as the floating photocatalyst under natural sunlight observing comparable 91% degradation efficiency in 100 min with that of 99% efficiency in the UV light-illuminated slurry system. The formation of petals-like structures, defects from the liberation of DMF molecules from the ZnO surface by calcination, larger pore sizes and pore volumes provided a synergistic effect on enhancing the degradation efficiency in these cases.

Functionalized graphene oxide-zinc oxide hybrid material and its deployment for adsorptive removal of levofloxacin from aqueous media

This work reports on the synthesis of aspartic acid-functionalized graphene oxide-zinc oxide, as a functional porous material, and its potential to mitigate levofloxacin (LFXN). The adsorbent was characterized by various techniques, including ultraviolet-visible (UV-Vis), Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM). The average crystallite size of the prepared composite was about 17.30 nm. Batch adsorption studies were carried out to elucidate the adsorption process for LFXN. Different parameters, including contact time, LFXN initial concentration, adsorbent concentration, pH, temperature, and ionic strength were studied. The mechanism and kinetics were studied by fitting the data to Freundlich and Langmuir isotherms, pseudo-first-order and pseudo-second-order kinetic models, respectively. The isotherm data was better fitted to Langmuir isotherm (R² = 0.999) as compared to the Freundlich model. The maximum adsorption capacity obtained at equilibrium was 73.15 mg/g. For kinetic studies, Pseudo first order was better fitted with R² = 0.87797, confirming the physisorption process. Thermodynamics parameters revealed that the process was exothermic and spontaneous at low temperatures. The adsorption mechanism was studied and the impregnation of LFXN in the adsorbent was confirmed by FTIR studies. This research proved that the designed GO/Asp-ZnO was a novel and promising adsorbent for the removal of LFXN with an efficiency of 95.12% at 30 mg/L LFXN by 0.6 g/L adsorbent in 24 h at pH = 7 and T = 25 °C.

Self-Organization Effects of Thin ZnO Layers on the Surface of Porous Silicon by Formation of Energetically Stable Nanostructures

The formation of complex surface morphology of a multilayer structure, the processes of which are based on quantum phenomena, is a promising domain of the research. A hierarchy of pore of various sizes was determined in the initial sample of porous silicon by the atomic force microscopy. After film deposition by spray pyrolysis, ZnO nanoclusters regularly distributed over the sample surface were formed. Using the electron paramagnetic resonance (EPR) method it was determined that the localization of paramagnetic centers occurs more efficiently as a result of the ZnO deposition. An increase in the number of deposited layers, leads to a decrease in the paramagnetic center relaxation time, which is probably connected with the formation of ZnO nanocrystals with energetically stable properties. The nucleation and formation of nanocrystals is associated with the interaction of particles with an uncompensated charge. There is no single approach to determine the mechanism of this process. By the EPR method supplemented with the signal cyclic saturation, spectral manifestations from individual centers were effectively separated. Based on electron paramagnetic resonance and photoluminescence studies it was revealed that the main transitions between energy levels are due to oxygen vacancies and excitons.

Effective Antibacterial/Photocatalytic Activity of ZnO Nanomaterials Synthesized under Low Temperature and Alkaline Conditions

The purpose of this study was to evaluate the surface properties of ZnO nanomaterials based on their ability to photodegrade methyl blue dye (MB) and to show their antibacterial properties against different types of Gram-positive bacteria (Bacillus manliponensis, Micrococcus luteus, Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). In this study, ZnO nanomaterials were synthesized rapidly and easily in the presence of 1-4 M NaOH at a low temperature of 40 °C within 4 h. It was found that the ZnO nanomaterials obtained from the 1.0 M (ZnO-1M) and 2.0 M (ZnO-2M) aqueous solutions of NaOH had spherical and needle-shaped forms, respectively. As the concentration of NaOH increased, needle thickness increased and the particles became rod-like. Although the ZnO nanomaterial shapes were different, the bandgap size remained almost unchanged. However, as the NaOH concentration increased, the energy position of the conduction band shifted upward. Photo current curves and photoluminescence intensities suggested that the recombination between photoexcited electrons and holes was low in the ZnO-4M materials prepared in 4.0 M NaOH solution; however, charge transfer was easy. ∙O₂^- radicals were generated more than ∙OH radicals in ZnO-4M particles, showing stronger antibacterial activity against both Gram-positive and Gram-negative bacteria and stronger decomposition ability on MB dye. The results of this study suggest that on the ZnO nanomaterial surface, ∙O₂^- radicals generated are more critical for antibacterial activity than particle shape.

Bacterial Surface Disturbances Affecting Cell Function during Exposure to Three-Compound Nanocomposites Based on Graphene Materials

Combating pathogenic microorganisms in an era of ever-increasing drug resistance is crucial. The aim of the study was to evaluate the antibacterial mechanism of three-compound nanocomposites that were based on graphene materials. To determine the nanomaterials' physicochemical properties, an analysis of the mean hydrodynamic diameter and zeta potential, transmission electron microscope (TEM) visualization and an FT-IR analysis were performed. The nanocomposites' activity toward bacteria species was defined by viability, colony forming units, conductivity and surface charge, cell wall integrity, ATP concentration, and intracellular pH. To ensure the safe usage of nanocomposites, the presence of cytokines was also analyzed. Both the graphene and graphene oxide (GO) nanocomposites exhibited a high antibacterial effect toward all bacteria species (Enterobacter cloacae, Listeria monocytogenes, Salmonella enterica, and Staphylococcus aureus), as well as exceeded values obtained from exposure to single nanoparticles. Nanocomposites caused the biggest membrane damage, along with ATP depletion. Nanocomposites that were based on GO resulted in lower toxicity to the cell line. In view of the many aspects that must be considered when investigating such complex structures as are three-component nanocomposites, studies of their mechanism of action are crucial to their potential antibacterial use.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV-vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10^-4), s-SWCNT (3.4 × 10^-4), and p-SWCNT (2 × 10^-4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

Template-directed synthesis of pomegranate-shaped zinc oxide@zeolitic imidazolate framework for visible light photocatalytic degradation of tetracycline

The development of photocatalysts for efficient tetracycline (TC) degradation under visible light is urgently needed yet remains a great challenge. Most semiconductor photocatalysts with low specific surface area are easy to agglomerate in solution and unfavorable for enriching pollutants. Herein, we present the preparation of pomegranate-shaped zinc oxide@zeolitic imidazolate framework (ZnO@ZIF-8) by in situ growth of ZIF-8 on a petal-shaped ZnO template that enhances the adsorption and photocatalytic degradation of TC. ZnO@ZIF-8 exhibits an excellent photostability and a TC photodegradation efficiency of 91% under visible light (λ > 420 nm) in 50 min at room temperature, which can be recycled over five times without any loss of activity. Moreover, the plausible photocatalysis reaction mechanism and the degradation intermediates are elucidated with the aid of three-dimensional excitation-emission matrix spectra and liquid chromatography-mass spectrometry system. This study offers new insights into the design of antibiotic degradation photocatalysts and the development of photocatalysts with broad-spectrum responses for efficient TC elimination.

Advances in nanomaterials for heterogeneous photocatalysis

Photocatalysis method for environmental applications has been using for a long time. This review article traces back the origin of catalysis, its classification and journey of development to heterogeneous photocatalysis and the article’s novelty is in the simplicity, and easily understandable language, designed for the beginners. These heterogeneous photocatalysts are grouped into eleven different categories. As the paper is focused on photocatalysis, an insight on fundamental principles and mechanisms of photocatalysis are explained systematically with schematic illustrations and reactions that take place during redox- oxidation and reduction reactions in photocatalysis. With an approach towards utilizing green energy and expanding the photocatalyst’ absorption wavelength range towards the visible regime, bandgap engineering techniques by adopting doping and hetero-structures are explained with examples of different materials. In addition, dominating factors of photocatalysis reaction viz. composition of a heterogeneous photocatalyst, doping, hetero-structures, pH, surface defects on photocatalysis reaction are explored, focussing on variable charge transfer mechanisms. The main influencing factor in generating reactive oxygen species is pH of the photocatalysis reaction and are studied indetail. The effect of alkalinity or acidity in catalyst surfaces and molecular interaction depending upon the point zero charges of the photocatalyst are discussed. For the better study of catalyst properties, careful analysis and study is a much-needed field as a scope for further improvement. Hence, this article will guide a beginner to understand the photocatalysis topic with ease.

Eco-Friendly Photocatalysts for Degradation of Dyes

In the current era of globalization, synthetic dyes are one of the key factors of water pollution. Photocatalysis constitutes a promising technology for the treatment of wastewater, especially to those containing hard-to-remove organic compounds. Zinc oxide nanoparticles (ZnONPs) play a vital role as a photocatalyst material. This research highlights the synthesized ZnONPs with roselle flower and oil palm leaf extract. The extracts and sodium hydroxide (NaOH) act as reducing agents during the synthesis process. Synthesis without the addition of plant extract is used as blank control for the experiment. Structural and optical studies of the three variants of ZnONPs were performed. High purity of ZnONPs with element Zn and O was obtained. The size of the three variants of ZnONPs was from 10–15 nm and found in agglomerated spherical shape. Large band gap, 3.2 eV was obtained by UV-Vis and high thermal stability was proven by TGA. Oxygen vacancies that assist in the degradation phenomenon were found in ZnONPs. Five percent of ZnONPs with the presence of 10 W UV light could effectively degrade 10 ppm MO in 5 h and MB in 3 h. Besides, high antioxidant properties and low toxicity demonstrated the ability of ZnONPs to be used as photocatalysts. In conclusion, ZnONPs can be further developed for pharmaceutical and industrial use.