A facile route to reduced graphene oxide–zinc oxide nanorod composites with enhanced photocatalytic activity

Synthesis of carboxylated cellulose nanocrystal/ZnO nanohybrids using Oxytenanthera abyssinica cellulose and zinc nitrate hexahydrate for radical scavenging, photocatalytic, and antibacterial activities

The extremely low antioxidant, photocatalytic, and antibacterial properties of cellulose limit its application in the biomedical and environmental sectors. To improve these properties, nanohybrides were prepared by mixing carboxylated cellulose nanocrystals (CCNCs) and zinc nitrate hexahydrate. Data from FTIR, XRD, DLS, and SEM spectra showed that, ZnO nanoparticles, with a size ranging from 94 to 351 nm and the smallest nanoparticle size of 164.18 nm, were loaded onto CCNCs. CCNCs/ZnO1 nanohybrids demonstrated superior antibacterial, photocatalytic, and antioxidant performance. More considerable antibacterial activity was shown with a zone of inhibition ranging from 26.00 ± 1.00 to 40.33 ± 2.08 mm and from 31.66 ± 3.51 to 41.33 ± 1.15 mm against Gram-positive and Gram-negative bacteria, respectively. Regarding photodegradation properties, the maximum value (∼91.52 %) of photocatalytic methylene blue degradation was observed after 75 min exposure to a UV lamp. At a concentration of 125.00 μm/ml of the CCNC/ZnO1 nanohybrids sample, 53.15 ± 1.03 % DPPH scavenging activity was obtained with an IC50 value of 117.66 μm/ml. A facile, cost-effective, one-step synthesis technique was applied to fabricate CCNCs/ZnO nanohybrids at mild temperature using Oxytenanthera abyssinica carboxylated cellulose nanocrystals as biotemplate. The result showed that CCNCs/ZnO nanohybrids possess potential applications in developing advanced functional materials for dye removal and antibacterial and antioxidant applications.

Silica sand-supported nano zinc oxide-graphene oxide composite induced rapid photocatalytic decolorization of azo dyes under sunlight and improved antimicrobial activity

Here, silica sand-supported heterojunction composite of nano zinc oxide (nZnO) and graphene oxide nanosheet (nZnO-GO@SS) was prepared, and its potential as an efficient photocatalyst for the degradation of methylene blue (MB) and Rhodamine-B (Rh-B) under sunlight was demonstrated. Transmission electron microscopy confirmed the uniform distribution of spherically shaped nZnO of average size of approximately 8 nm over graphene oxide nanosheet (GO) in the composites. Photodegradation yields of 95.3% and 97.5% for 100 ppm of MB and Rh-B dye within 150 and 220 min, respectively, were achieved under sunlight by the prepared nanocatalyst (nZnO-GO), while sand microparticle-supported nanocatalyst (nZnO-GO@SS) demonstrated faster degradation of MB and Rh-B, i.e., within 120 and 160 min, respectively. Furthermore, when the recyclability of the photocatalyst was studied, the nZnO-GO exhibited more than 80% degradation efficiency after five cycles for both the dyes and nZnO-GO@SS demonstrated 10% higher (~90%) removal capability after five cycles of reuse. Furthermore, the antibacterial assay showed complete inactivation of Escherichia coli and Staphylococcus aureus bacterial strain by nZnO-GO@SS. Hence, our proposed strategy for the removal of toxic dyes from the aquatic environment under sunlight proved that sand microparticle-supported nanocatalyst (nZnO-GO@SS) might be a superior, cost-effective, and suitable photocatalytic system for industrial applications toward toxic dye removal and decontamination from industrial wastewater.

Comparative Degradation Studies of Carmine Dye by Photocatalysis and Photoelectrochemical Oxidation Processes in the Presence of Graphene/N-Doped ZnO Nanostructures

The goal of this study was to synthesize a UV-light-active ZnO photocatalyst by modifying it with nitrogen and graphene, then applying it to the degradation of carmine dye utilizing two promising technologies: photocatalysis and electrochemical oxidation (E.O.). Different techniques were used to analyze the prepared photocatalysts, such as Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). According to XRD measurements, the produced nanocomposite possesses a hexagonal wurtzite structure, indicating ZnO and markedly crystalline. For photocatalytic applications, the results revealed that the 0.001 g of G/N-doped ZnO catalyst achieved 66.76% degradation of carmine and kinetic degradation rates of 0.007 min−1 within 185 min by photocatalysis under UV light irradiation. In comparison, the same sample reached 100% degradation of carmine and kinetic degradation rates of 0.202 min−1 within 15 min using the electrochemical oxidation method. The improved photocatalytic activity of as-produced nanocomposites can be attributed to intermediate levels in the prohibited bandgap energy and the enhanced oxygen vacancies caused by nitrogen doping. The electrolyte (NaCl) on the degradation of the carmine dye was tested, and the findings indicated that the dye molecules were photodegraded by the 0.001 g of G/N-doped ZnO nanocomposite after a 15 min time interval. The data presented in this work for the carmine breakdown in water give intriguing contrasts between photocatalytic, indirect electrochemical oxidation, and photoelectrochemical oxidation. The action of chlorinated oxidative species, predominantly HClO, which were electrogenerated at the electrode surface due to the chloride ion’s oxidation in solution, induced indirect electrochemical oxidation degradation. This study also revealed that the modifications made to ZnO were beneficial by improving its photocatalytic activities under UV light, as well as a comparison of photocatalysis and electrochemical oxidation processes to determine which technique is best for treating carmine in effluents with high chloride ions.

Synthesis, Characterization and Enhanced Visible Light Photocatalytic Performance of ZnWO4-NPs@rGO Nanocomposites

ZnWO4 nanoparticles on reduced graphene oxide (ZnWO4-NPs@rGO) nanocomposites were synthesized using the hydrothermal method. Structural, morphological, optical, and photocatalytic studies of the ZnWO4-NPs@rGO nanocomposites were successfully investigated. Photo-catalytic performances of the ZnWO4-NPs@rGO nanocomposites were examined for the degradation of hazardous methylene blue dye (HMBD) in a neutral medium. ZnWO4-NPs@rGO nanocomposites show superior photo-catalytic performances over pure ZnWO4 nanoparticles. ZnWO4-NPs@rGO nanocomposites degrade ~98% dye while pure ZnWO4 nanoparticles degrade ~53% dye in 120 min. The prepared nanocomposites also show excellent recycled photo-catalytic efficiencies over multiple cycles.

A superfine glass fibre air filter with rapid response to photocatalytic antibacterial properties under visible light by loading rGO/ZnO

The development of high-performance air filter has become more and more important to public health. However, it has always been very challenging for developing a multifunctional air filter to simultaneously achieve excellent filtration and antibacterial properties. Herein, a versatile air filter was prepared with loading the reduced graphene (rGO) and zinc oxide on the superfine glass fibre (s-GF) with the three-dimensional network structure by in situ sol-gel process followed by calcination, which aims to achieve synergistic high-efficiency air filtration and rapid response to photocatalytic antibacterial properties under visible light. The air filter showed a three-dimensional network structure based on a rGO/ZnO/s-GF multilayer and exhibited the highest catalytic performance by achieving a 95% degradation effect on rhodamine B within 2 h and achieving 100% antibacterial inactivation of the Escherichia coli and Staphylococcus aureus within 4 h under visible light when the weight ratio of rGO in rGO/ZnO is 1.6%. The air filtration efficiency can also be maintained at 99% after loading ZnO and rGO photocatalytic particles. The spectrum of the photoluminescence (PL), UV-Vis diffuse reflectance spectra (DRS) and electron spin resonance (ESR) indicate that the combination of rGO and ZnO on the s-GF can increase the separation of photogenerated carriers and the specific surface area of the air filter, thereby increasing the photocatalytic response and antibacterial properties of the s-GF air filter under visible light in a short time.

High-throughput Production of ZnO-MoS2-Graphene Heterostructures for Highly Efficient Photocatalytic Hydrogen Evolution

High-throughput production of highly efficient photocatalysts for hydrogen evolution remains a considerable challenge for materials scientists. Here, we produced extremely uniform high-quality graphene and molybdenum disulfide (MoS2) nanoplatelets through the electrochemical-assisted liquid-phase exfoliation, out of which we subsequently fabricated MoS2/graphene van der Waals heterostructures. Ultimately, zinc oxide (ZnO) nanoparticles were deposited into these two-dimensional heterostructures to produce an artificial ZnO/MoS2/graphene nanocomposite. This new composite experimentally exhibited an excellent photocatalytic efficiency in hydrogen evolution under the sunlight illumination ( λ > 400   n m ), owing to the extremely high electron mobilities in graphene nanoplatelets and the significant visible-light absorptions of MoS2. Moreover, due to the synergistic effects in MoS2 and graphene, the lifetime of excited carriers increased dramatically, which considerably improved the photocatalytic efficiency of the ZnO/MoS2/graphene heterostructure. We conclude that the novel artificial heterostructure presented here shows great potential for the high-efficient photocatalytic hydrogen generation and the high throughput production of visible-light photocatalysts for industrial applications.

Sonochemical assisted synthesis of RGO/ZnO nanowire arrays for photoelectrochemical water splitting

This article presented the synthesis of a hybrid nanoarchitecture material composed of reduced graphene oxide (RGO) multiple sheets and ZnO nanowire arrays (NWAs) formed on an arbitrary ZnO coated fluorine doped tin oxide (FTO) substrates via pulse sonication and hydrothermal approach. The NWAs have high aspect-ratio, high density, apt positioning and well-ordered formation. FESEM images demonstrated that RGO layers have been effectively intercalated between and on the accessible surfaces of the ZnO NWAs. The diameter of ZnO nanowires is 80-150nm and length about 1-2μm. Raman spectrum of hybrid material exhibited characteristic D and suppressed G peaks for graphene and E₂ mode at 437cm^-1 for ZnO NWAs. UV-visible spectrum indicated slight red shift towards visible range after formation of RGO/ZnO NWAs heterostructure. The Photoelectrochemical results indicated higher current densities for RGO/ZnO NWAs heterostructure due to water oxidation reaction at the working electrode compared to pristine ZnO NWAs.

Extraction of nanocellulose and in-situ casting of ZnO/cellulose nanocomposite with enhanced photocatalytic and antibacterial activity

Polymer hosted metallic nanostructures with diverse applications have become a prominent area of materials science, engineering and technology. In this study nanocellulose (NC) was synthesized from oil palm empty fruit bunches biomass via alkaline treatment and acid hydrolysis and characterized. The obtained NC was used as a host polymer for the synthesis of zinc oxide (ZnO) nanostructures through in-situ solution casting method. Alkaline treatment and acid hydrolysis increased the percentage crystalline index from 35.7% to 43.3% and 53.3% respectively. X-ray diffraction studies pointed to cellulose I, with a monoclinic structure. Zinc oxide/cellulose nanocomposite displayed more photocatalytic activity than pure ZnO nanostructures upon degradation of methylene blue, and also improved antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.

Role of RGO support and irradiation source on the photocatalytic activity of CdS-ZnO semiconductor nanostructures

Photocatalytic activity of semiconductor nanostructures is gaining much importance in recent years in both energy and environmental applications. However, several parameters play a crucial role in enhancing or suppressing the photocatalytic activity through, for example, modifying the band gap energy positions, influencing the generation and transport of charge carriers and altering the recombination rate. In this regard, physical parameters such as the support material and the irradiation source can also have significant effect on the activity of the photocatalysts. In this work, we have investigated the role of reduced graphene oxide (RGO) support and the irradiation source on mixed metal chalcogenide semiconductor (CdS-ZnO) nanostructures. The photocatalyst material was synthesized using a facile hydrothermal method and thoroughly characterized using different spectroscopic and microscopic techniques. The photocatalytic activity was evaluated by studying the degradation of a model dye (methyl orange, MO) under visible light (only) irradiation and under natural sunlight. The results reveal that the RGO-supported CdS-ZnO photocatalyst performs considerably better than the unsupported CdS-ZnO nanostructures. In addition, both the catalysts perform significantly better under natural sunlight than under visible light (only) irradiation. In essence, this work paves way for tailoring the photocatalytic activity of semiconductor nanostructures.

Porous VO(x)N(y) nanoribbons supported on CNTs as efficient and stable non-noble electrocatalysts for the oxygen reduction reaction

Novel nanocomposites of carbon nanotubes supported porous VO_xN_y nonoribbons (VO_xN_y-CNTs) have been synthesized by the annealing of the sol-gel mixture of CNTs and V₂O₅ under NH₃ atmosphere as well as the ageing process in air. Besides the morphological and structural characterizations revealed by TEM, SEAD, EDS, XRD and XPS measurements, typical electrochemical tests including cyclic voltammetry (CV), rotating disk electrode (RDE) and chronoamperometry have been employed to determine the oxygen reduction reaction (ORR) performance of VO_xN_y-CNTs. Inspiringly, the results indicate that VO_xN_y-CNTs catalyst exhibits a 0.4 mA/cm² larger diffusion-limited current density, a 0.10  V smaller onset potential value, a 10.73% less of ORR current decay and an excellent methanol-tolerance compared with commercial Pt/C catalyst. Therefore, we have reasonable grounds to believe that this new VO_xN_y-CNTs nanocomposites can be regarded as a promising non-precious methanol-tolerant ORR catalyst candidate for alkaline fuel cells.

Novel VN/C nanocomposites as methanol-tolerant oxygen reduction electrocatalyst in alkaline electrolyte

A novel VN/C nanostructure consisting of VN nanoparticles and graphite-dominant carbon layers is synthesized by nitridation of V₂O₅ using melamine as reductant under inert atmosphere. High crystalline VN nanoparticles are observed to be uniformly distributed in carbon layers with an average size of ca13.45 nm. Moreover, the electrocatalytic performance of VN/C towards oxygen reduction reaction (ORR) in alkaline electrolyte is fascinating. The results show that VN/C has a considerable ORR activity, including a 75 percent value of the diffusion-limited current density and a 0.11 V smaller value about the onset potential with respect to Pt/C catalyst. Moreover, the excellent methanol-tolerance performance of VN/C has also been verified with 3 M methanol. Combined with the competitive prices, this VN/C nanocomposite can serve as an appropriate non-precious methanol-tolerant ORR catalyst for alkaline fuel cells.

Facile synthesis and photocatalytic properties of ZnO core/ZnS–CdS solid solution shell nanorods grown vertically on reductive graphene oxide

The synthesis of ZnO core/Zn_xCd_1−xS shell nanorods grown vertically on RGO sheets and the important role played by Zn_xCd_1−xS on photocatalytic activity are described.