NiO-nanoflakes grafted graphene: an excellent photocatalyst and a novel nanomaterial for achieving complete pathogen control

Hybrid nanostructures exhibiting both photocatalytic and antibacterial activity-a review

The most vital issues of the modern world for a sustainable future are "health" and "the environment." Scientific endeavors to tackle these two major concerns for mankind need serious attention. The photocatalytic activity toward curbing environmental pollution and antibacterial performance toward a healthy society are two directions that have been emphasized for decades. Recently, materials engineering, in their nanodimension, has shown tremendous possibilities to integrate these functionalities within the same materials. In particular, hybrid nanostructures have shown magnificent prospects to combat both crucial challenges. Many researchers are separately engaged in this important field of research but the collective knowledge on this domain which can facilitate them to excel is badly missing. The present article integrates the development of different hybrid nanostructures which exhibit both photocatalytic degradations of environmental pollutants and antibacterial efficiency. Various synthesis techniques of those hybrid nanomaterials have been discussed. Hybrid nanosystems based on several successful materials have been categorically discussed for better insight into the research advancement in this direction. In particular, Ag-based, metal oxides-based, layered carbon material-based, and Mexene- and self-cleaning-based materials have been chosen for detailing their performance as anti-pollutant and antibacterial materials. Those hybrid systems along with some miscellaneous booming nanostructured materials have been discussed comprehensively with their success and limitations toward their bifunctionality as antipollutant and antibacterial agents.

Facile Synthesis of La- and Chitosan-Doped CaO Nanoparticles and Their Evaluation for Catalytic and Antimicrobial Potential with Molecular Docking Studies

In the current study, a low-cost and straightforward coprecipitation technique was adopted to synthesize CaO and La-doped CS/CaO NPs. Different weight ratios (2 and 4) of La were doped into fixed amounts of CS and CaO. Synthesized samples exhibited outstanding catalytic performance by degrading methylene blue (MB) in a highly efficient manner. The X-ray diffraction technique detected the presence of a cubic phase of CaO and a decrease in crystallite size of the samples with the addition of La. Fourier transform infrared spectroscopy confirmed the presence of the dopant and the base material with functional groups at 712 cm^-1. A decrease in the absorption intensity of doped CaO was observed with an increasing amount of dopants La and CS accompanied by a blueshift leading to an increase in the band gap energy from 4.17 to 4.42 eV, as recorded with an ultraviolet-visible spectrophotometer. The presence of dopants (La and CS) and the evaluation of the elemental constitution of Ca and O were supported with the energy-dispersive spectroscopy technique. In an acidic medium, the catalytic activity against the MB dye was reduced (93.8%) for 4% La-doped CS/CaO. For La-doped CS/CaO, vast inhibition domains ranged within 4.15-4.70 and 5.82-8.05 mm against Escherichia coli while 4.15-5.20 and 6.65-13.10 mm against Staphylococcus aureus (S. aureus) at the least and maximum concentrations, correspondingly. In silico molecular docking studies suggested these nanocomposites of chitosan as possible inhibitors against the enoyl-acyl carrier protein reductase (FabI) from S. aureus.

Ultrahigh-efficiency antibacterial and adsorption performance induced by copper-substituted polyoxomolybdate-decorated graphene oxide nanocomposites

Given the rise of drug-resistant pathogens and industrial contaminants, the development of efficient and eco-friendly water treatment technologies and materials is highly desirable and urgent. Herein, a multifunctional graphene oxide/chitosan/copper-based polyoxometalate (GO/CS/Cu-POM) nanocomposite (Cu-POM, [Cu(L)₄][Cu(L)₃(H₂O)][Cu(L)(H₂O)][P₂Mo₅O₂₃]·4H₂O, L = pyrazole) was synthesized by the ultrasound-assisted self-assembly strategy. The GO/CS/Cu-POM nanocomposite exhibited potent bactericidal properties against gram-positive/negative bacterial strains Staphylococcus aureus (S. aureus, 99.98%), Escherichia coli (E. coli, 99.99%), and drug-resistant E. coli bacterial strains (kanamycin-resistant E. coli 99.93% and ampicillin-resistant E. coli, 97.94%). Further, the antibacterial performance was strongly dependent on synergistic effect between GO/CS and Cu-POM in GO/CS/Cu-POM. The destruction of bacterial membrane and high levels of oxidative stress induced by GO/CS/Cu-POM played a significant role in the bactericidal process. Furthermore, the GO/CS/Cu-POM nanocomposite also displayed superior performance for removal of methylene blue (MB, 96.86%), gentian violet (GV, 97.77%), basic fuchsin (BF, 96.47%), tetracycline (TC, 78.92%) and norfloxacin (NC, 76.26%). Moreover, the main process of dye removal by GO/CS/Cu-POM was controlled by chemisorption. More importantly, the GO/CS/Cu-POM nanocomposite indicated good biocompatibility to human umbilical vein endothelial cells. Current work provides an effective strategy to design multifunctional POM-based composites for water purification and environmental protection.

SnO2nanorods/graphene nanoplatelets nanocomposites: towards fast removal of malachite green and pathogen control

The world is facing alarming challenges of environmental pollution due to uncontrolled water contamination and multiple drug resistance of pathogens. However, these challenges can be addressed by using novel nanocomposites materials such as, SnO₂/graphene nanopaletelets (GNPs) nanocomposites remarkably. In this work, we have prepared SnO₂nanorods and SnO₂/GNPs nanocomposites (GS-I and GS-II) with size of 25 ± 6 nm in length and 4 ± 2 nm in diameter. The optical bandgap energies change from 3.14 eV to 2.80 eV in SnO₂and SnO₂/GNPs nanocomposite. We found that SnO₂/GNPs nanocomposite (GS-II) completely removes (99.11%) malachite green in 12 min, under UV light exposure, while under same conditions, SnO₂nanorods removes only 37% dye. Moreover, visible light exposure resulted in 99.01% removal of malachite green in 15 min by GSII as compared to 24.7% removal by SnO₂. In addition, GS-II nanocomposite inhibits 79.57% and 78.51% growth ofP. aeruginosaandS. aureusrespectively. A synchronized contribution of SnO₂and GNPs makes SnO₂/GNPs nanocomposites (GS-II) an innovative multifunctional material for simultaneous fast and complete removal of malachite green and inhibition of drug resistant pathogens.

Novel Structures and Applications of Graphene-Based Semiconductor Photocatalysts: Faceted Particles, Photonic Crystals, Antimicrobial and Magnetic Properties

Graphene, graphene oxide, reduced graphene oxide and their composites with various compounds/materials have high potential for substantial impact as cheap photocatalysts, which is essential to meet the demands of global activity, offering the advantage of utilizing “green” solar energy. Accordingly, graphene-based materials might help to reduce reliance on fossil fuel supplies and facile remediation routes to achieve clean environment and pure water. This review presents recent developments of graphene-based semiconductor photocatalysts, including novel composites with faceted particles, photonic crystals, and nanotubes/nanowires, where the enhancement of activity mechanism is associated with a synergistic effect resulting from the presence of graphene structure. Moreover, antimicrobial potential (highly needed these days), and facile recovery/reuse of photocatalysts by magnetic field have been addresses as very important issue for future commercialization. It is believed that graphene materials should be available soon in the market, especially because of constantly decreasing prices of graphene, vis response, excellent charge transfer ability, and thus high and broad photocatalytic activity against both organic pollutants and microorganisms.

Unravelling the interfacial interaction in mesoporous SiO2@nickel phyllosilicate/TiO2 core-shell nanostructures for photocatalytic activity

Core-shell based nanostructures are attractive candidates for photocatalysis owing to their tunable physicochemical properties, their interfacial contact effects, and their efficacy in charge-carrier separation. This study reports, for the first time, on the synthesis of mesoporous silica@nickel phyllosilicate/titania (mSiO₂@NiPS/TiO₂) core-shell nanostructures. The TEM results showed that the mSiO₂@NiPS composite has a core-shell nanostructure with a unique flake-like shell morphology. XPS analysis revealed the successful formation of 1:1 nickel phyllosilicate on the SiO₂ surface. The addition of TiO₂ to the mSiO₂@NiPS yielded the mSiO₂@NiPS/TiO₂ composite. The bandgap energy of mSiO₂@NiPS and of mSiO₂@NiPS/TiO₂ were estimated to be 2.05 and 2.68 eV, respectively, indicating the role of titania in tuning the optoelectronic properties of the SiO₂@nickel phyllosilicate. As a proof of concept, the core-shell nanostructures were used as photocatalysts for the degradation of methyl violet dye and the degradation efficiencies were found to be 72% and 99% for the mSiO₂@NiPS and the mSiO₂@NiPS/TiO₂ nanostructures, respectively. Furthermore, a recyclability test revealed good stability and recyclability of the mSiO₂@NiPS/TiO₂ photocatalyst with a degradation efficacy of 93% after three cycles. The porous flake-like morphology of the nickel phyllosilicate acted as a suitable support for the TiO₂ nanoparticles. Further, a coating of TiO₂ on the mSiO₂@NiPS surface greatly affected the surface features and optoelectronic properties of the core-shell nanostructure and yielded superior photocatalytic properties.

ZnxCd1-xS/g-C3N4 nanocomposites: synthesis, characterization, and photocatalytic activity

In this work, we prepared ZnxCd1-xS/g-C3N4 nanocomposites with excellent catalytic effect by the simple chemical precipitation method. The ZnxCd1-xS/g-C3N4 composite with excellent effect of degrading methylene blue (MB) was prepared by adjusting the ratio of Zn to Cd. The Zn0.25Cd0.75S/g-C3N4 nanocomposites have the highest degradation efficiency, which can reach 92.25%. The specific surface area and visible light absorption range are increased by the synergistic effect of the combination of ZnxCd1-xS and g-C3N4. The ZnxCd1-xS/g-C3N4 nanocomposites prepared by this study with excellent photocatalytic properties provide a method for the preparation of new composite materials in the future.

Bimetallic Ag/Cu incorporated into chemically exfoliated MoS2 nanosheets to enhance its antibacterial potential: in silico molecular docking studies

Bimetallic Ag and Cu (1:1 wt%) nanoparticles (NPs) were synthesized and annealed at temperatures of 400 °C, 600 °C, and 800 °C using chemical reduction techniques. High temperature annealed (at 800 °C) Ag:Cu sample ratios (5 and 10 wt%) were used to dope MoS₂. A wide variety of techniques including X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning, high resolution transmission electron microscopy, differential scanning calorimetry, thermogravimetric analysis, Raman, photoluminescence, and ultraviolet visible spectrophotometry were used to study the morphology, structure, functional groups, excitons recombination, and thermal and optical properties of both annealed and doped samples. The antimicrobial activity of the prepared products was tested on the MRSA-superbug with ciprofloxacin antibiotic as the reference drug. Statistically significant (P < 0.05) inhibition zones (mm) were recorded for the as-synthesized Ag-Cu, heat-treated samples at 400 °C, 600 °C, and 800 °C, doped Ag-Cu/MoS₂ 5% and Ag-Cu/MoS₂ 10% which ranged from 6.35-9.85 mm and 8.60-11.75 mm at (0.5, 1.0 mg 50 μl^-1) concentrations compared with ciprofloxacin 12.55 mm and DIW 0 mm inhibition zones, respectively. Overall Ag-Cu NPs alone and with different temperature treatments showed less antibacterial efficacy compared with Ag-Cu/MoS₂ 5% and 10%. Furthermore, molecular docking studies were employed to unveil the binding interaction pattern of NPs in the active pocket of β-lactamase enzyme suggested that it could be a potential inhibitor that could be further evaluated for its enzyme inhibition characteristics.

Surfactant-Free Aqueous Dispersions of Shape- and Size-Controlled Zirconia Colloidal Nanocrystal Clusters with Enhanced Photocatalytic Activity

Colloidal nanocrystal clusters (CNCs) are formed by clustering nanocrystals into secondary structures, which represent a new class of materials and have attracted considerable attention, owing to their unique collective properties and novel functionalities achieved from the ensembles in addition to the properties of each individual subunit. Here, we design a simple route to prepare aqueous dispersions of highly stable ZrO₂ CNCs with tunable shape and size without modification. ZrO₂ CNCs are composed of many ZrO₂ nanocrystals each with a size of about 7 nm and possess a mesoporous structure. Both cube-like and star-like shapes of CNCs can be achieved by using different alkaline sources, while the size of CNCs can be adjusted by changing the hydrothermal time. The as-prepared aqueous dispersions of ZrO₂ CNCs display an enhanced photocatalytic activity in the degradation of rhodamine B (RhB), compared with ZrO₂ nanodispersions. More interestingly, star-like ZrO₂ CNCs show better photocatalytic degradation properties than those of cube-like counterparts and even commercial P25. Furthermore, ZrO₂ CNCs are easily recycled and can be used for the degradation of a range of dye systems.

Powerful antibacterial activity of graphene/nanoflower-like nickelous hydroxide nanocomposites

Aim: The development of new and efficient antibacterial agents is urgent to overcome emerging antimicrobial resistance. Materials & methods: Herein, we have presented a new type of 3D antibacterial system to prompt bacteria to contact with the any plane of nanocomposites. Results: Comparing the antibacterial activity of graphene oxide, reduced graphene oxide and graphene-loaded nanoflower-like nickelous hydroxide (GN/Ni(OH)2) nanocomposites; the GN/Ni(OH)2 showed stronger bactericidal capability toward Gram-negative/-positive bacteria. Moreover, the GN/Ni(OH)2 with low cytotoxicity can promote it as ‘green’ antimicrobial agents. And, the GN/Ni(OH)2 presented long-term stable antibacterial effectiveness after 2-month storage. The antibacterial mechanisms of GN/Ni(OH)2 were evidenced as the 3D contact and violent damage to the bacterial structure. Conclusion: The GN/Ni(OH)2 provides new insights into the antibacterial properties of 3D nanocomposites for effectively fighting pathogen threats in biomedicine and public health.