Ecofriendly sol-gel-derived dye-sensitized solar cells with aluminium-doped tin oxide photoanode

The manuscript reports the fabrication of an eco-friendly sol gel dye-sensitized solar cell (DSSC) based on aluminium (Al)-doped tin oxide nanoparticles with different concentrations (0.5, 1, and 5 mol%) of Al providing enhanced optical and electrical properties than its bare counterparts. The physical, chemical, optical, and electrical properties of the as-synthesized nanoparticles were studied using different analytical tools. X-ray diffraction (XRD) study reveals the crystal structure of the prepared samples ascribed to SnO2 nanoparticles uniformly with reduced crystallite size for Al-doped SnO2 nanoparticles. Field emission scanning electron microscope (FESEM) analysis reveals narrowing of particle size on doping with the Al, substantially enhancing the optical and surface characteristic features of the SnO2 nanoparticles. Photoconductivity studies indicate that all the samples have a good linear response with the increment of electric field in dark and photocurrent attributing to better photoconversion capability of the samples. Further, the optimized Al-doped SnO2 and bare SnO2 nanoparticles were subjected to sophisticated analytical studies such as high-resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS) for the better insight into their properties. The as-prepared Al-doped SnO2 nanoparticles in the present study record good optical, surface, and electrical properties which enhance their compatibility for possible photovoltaic applications especially in dye-sensitized solar cells as an environmentally safe alternate energy solution. Further, the current density-voltage (J-V) characteristics of the optimized Al-SnO2 and bare SnO2 photoanode component were probed for their suitability in DSSCs which disclosed enriched efficiency upon doping with aluminium nanoparticles.

Photocatalytic Performance of Undoped and Al-Doped ZnO Nanoparticles in the Degradation of Rhodamine B under UV-Visible Light:The Role of Defects and Morphology

Quasi-spherical undoped ZnO and Al-doped ZnO nanoparticles with different aluminum content, ranging from 0.5 to 5 at% of Al with respect to Zn, were synthesized. These nanoparticles were evaluated as photocatalysts in the photodegradation of the Rhodamine B (RhB) dye aqueous solution under UV-visible light irradiation. The undoped ZnO nanopowder annealed at 400 °C resulted in the highest degradation efficiency of ca. 81% after 4 h under green light irradiation (525 nm), in the presence of 5 mg of catalyst. The samples were characterized using ICP-OES, PXRD, TEM, FT-IR, ²⁷Al-MAS NMR, UV-Vis and steady-state PL. The effect of Al-doping on the phase structure, shape and particle size was also investigated. Additional information arose from the annealed nanomaterials under dynamic N₂ at different temperatures (400 and 550 °C). The position of aluminum in the ZnO lattice was identified by means of ²⁷Al-MAS NMR. FT-IR gave further information about the type of tetrahedral sites occupied by aluminum. Photoluminescence showed that the insertion of dopant increases the oxygen vacancies reducing the peroxide-like species responsible for photocatalysis. The annealing temperature helps increase the number of red-emitting centers up to 400 °C, while at 550 °C, the photocatalytic performance drops due to the aggregation tendency.

Drastic evolution of point defects in vertically grown ZnO nanorods induced by lithium ion implantation

The evolution of various point defects in 100 keV lithium (Li) ion-implanted ZnO nanorods (NRs) by varying the fluences from 1 × 10¹⁴ to 7 × 10¹⁵ ions per cm² has been investigated experimentally and using a simulation by stopping and range of ions in matter (SRIM). The X-ray photoelectron spectroscopy results indicate that the Li¹⁺ ions have been incorporated at Zn²⁺ sites, which forms Li_Zn acceptors in the implanted NRs. The structural disorder and the number of oxygen vacancies in the implanted ZnO NRs increase drastically with an increase in the Li fluence as indicated by the X-ray diffractometry and Raman scattering analyses. Both the formation of acceptors and implantation-induced defects make the Li-implanted NRs electrically highly resistive. The yellow-orange photoluminescence (PL) emission of the as-grown ZnO NRs has evolved into green emission in the implanted NRs. A suppression of the green PL at higher fluences is possibly due to an apparent decrease in the zinc vacancy concentration. The SRIM results explain the quantitative energy loss, the distributions of the implanted Li ions and the point defects along the target ZnO NRs. The consistency between the experimental and theoretical simulations validates our analyses on the formation and evolution of various point defects in highly resistive Li-implanted ZnO NRs.

Antimicrobial Effectiveness of Innovative Photocatalysts: A Review

Waterborne pathogens represent one of the most widespread environmental concerns. Conventional disinfection methods, including chlorination and UV, pose several operational and environmental problems; namely, formation of potentially hazardous disinfection by-products (DBPs) and high energy consumption. Therefore, there is high demand for effective, low-cost disinfection treatments. Among advanced oxidation processes, the photocatalytic process, a form of green technology, is becoming increasingly attractive. A systematic review was carried out on the synthesis, characterization, toxicity, and antimicrobial performance of innovative engineered photocatalysts. In recent decades, various engineered photocatalysts have been developed to overcome the limits of conventional photocatalysts using different synthesis methods, and these are discussed together with the main parameters influencing the process behaviors. The potential environmental risks of engineered photocatalysts are also addressed, considering the toxicity effects presented in the literature.

Enhanced Photoluminescence and Electrical Properties of n-Al-Doped ZnO Nanorods/p-B-Doped Diamond Heterojunction

The hydrothermal approach has been used to fabricate a heterojunction of n-aluminum-doped ZnO nanorods/p-B-doped diamond (n-Al:ZnO NRs/p-BDD). It exhibits a significant increase in photoluminescence (PL) intensity and a blue shift of the UV emission peak when compared to the n-ZnO NRs/p-BDD heterojunction. The current voltage (I-V) characteristics exhibit excellent rectifying behavior with a high rectification ratio of 838 at 5 V. The n-Al:ZnO NRs/p-BDD heterojunction shows a minimum turn-on voltage (0.27 V) and reverse leakage current (0.077 μA). The forward current of the n-Al:ZnO NRs/p-BDD heterojunction is more than 1300 times than that of the n-ZnO NRs/p-BDD heterojunction at 5 V. The ideality factor and the barrier height of the Al-doped device were found to decrease. The electrical transport behavior and carrier injection process of the n-Al:ZnO NRs/p-BDD heterojunction were analyzed through the equilibrium energy band diagrams and semiconductor theoretical models.

Lowering the onset potential of Zr-doped hematite nanocoral photoanodes by Al co-doping and surface modification with electrodeposited Co-Pi

Herein, in situ zirconium-doped hematite nanocoral (Zr-Fe₂O₃ (I) NC) photoanode was prepared via a specially designed diluted hydrothermal approach and modified with Al³⁺ co-doping and electrodeposited cobalt-phosphate ("Co-Pi") cocatalyst. Firstly, an unintentional in situ Zr-Fe₂O₃ (I)) NC photoanode was synthesized, which achieved an optimum photocurrent density of 0.27 mA/cm² at 1.0 V vs. RHE but possessed a more positively shifted onset potential than conventionally prepared hematite nanorod photoelectrodes. An optimized amount of aluminum co-doping suppresses the bulk as well as surface defects, which causes a negative shift in the onset potential from 0.85 V to 0.8 V vs. RHE and enhances the photocurrent density of Zr-Fe₂O₃(I) NC from 0.27 mA/cm² to 0.7 mA/cm² at 1.0 V vs. RHE. The electrodeposited Co-Pi modification further reduce the onset potential of Al co-doped Zr-Fe₂O₃(I) NC to 0.58 V vs. RHE and yield a maximum photocurrent of 1.1 mA/cm² at 1.0 V vs. RHE (1.8 mA/cm² at 1.23 V vs RHE). The improved photocurrent at low onset potential can be attributed to synergistic effect of Al co-doping and Co-Pi surface modification. Further, during photoelectrochemical water-splitting, a 137 and 67 μmol of hydrogen (H₂) and oxygen (O₂) evolution was achieved over the optimum Co-Pi-modified Al-co-doped Zr-Fe₂O₃(I) NC photoanode within 6 h. The proposed charge transfer mechanism in optimum Co-Pi-modified Alco-doped Zr-Fe₂O₃(I) NC photoanodes during the photoelectrochemical water splitting was also studied.

Sisal-like Sn2+ doped ZnO hierarchical structures: synthesis, growth mechanism, and their application in photocatalysis

Sisal-like Sn doped ZnO hierarchical structures were prepared by the hydrothermal method without employing templates or matrices. The architectures show enhanced light absorption, high photocatalytic properties, good stability and reusability.

Incorporating W cations into ZnO nanosheets: an efficient method towards ZnO/ZnWO4 photocatalysts for highly effective degradation of organic compounds under UV and visible-light irradiation

Novel ZnO/ZnWO₄ photocatalysts were synthesized for the removal of RhB dye with an excellent photocatalytic performance.

Size controlled, antimicrobial ZnO nanostructures produced by the microwave assisted route

Zinc oxide nanostructures (ZnO-NS) have shown to be of great value for several biological and biomedical applications. In particular, they have been used in bioimaging and delivery applications as well as inhibitors of microbial growth. In this work a new methodology for producing highly crystalline, size controlled ZnO-NS using a chemical microwave assisted synthetic route is described. A wide range of sizes and shapes of ZnO-NS could be controlled by varying the molar ratio of zinc nitrate to hexamethylenetetramine (HMT) from 3:20 to 30:20. The produced ZnO-NS systematically changed from 25 nm spherical nanoparticles to well-shaped micro sized hexagonal nanorods. Pronounced oxygen defects were also noticed, particularly at higher molar ratios. However, this is not the case with the lattice constant c, whose value is found to decrease by increasing this ratio. The produced ZnO-NS were tested as antimicrobial agent against Gram-negative (E. coli), Gram-positive (B. subtilis) bacteria and yeast (S. cerevisiae). Significant inhibition of these microbial strains was noticed even at low concentrations of ZnO-NS. The ZnO-NS with the molar ratio 3:20 was the most effective against the microbes tested. The results showed 80, 71 and 50% inhibition of E. coli, B. subtilis and S. cerevisiae, respectively. Using the "surfactant stress model" we describe the nanostructure formation of ZnO-NS. The antimicrobial activity of ZnO-NS correlated well with lattice constant c and particle size, where smaller particles with higher value of c displayed increase inhibitory activity. No clear correlation between the oxygen defects and bacterial inhibitions was observed. This highly crystalline, size tunable ZnO-NS could prove to be effective antimicrobial agents at low concentrations (e.g. 20 μg per 10 mL) and might be tested against other microorganisms.

Engineering Charge Transfer Characteristics in Hierarchical Cu₂S QDs @ ZnO Nanoneedles with p⁻n Heterojunctions: Towards Highly Efficient and Recyclable Photocatalysts

Equipped with staggered gap p-n heterojunctions, a new paradigm of photocatalysts based on hierarchically structured nano-match-shaped heterojunctions (NMSHs) Cu₂S quantum dots (QDs)@ZnO nanoneedles (NNs) are successfully developed via engineering the successive ionic layer adsorption and reaction (SILAR). Under UV and visible light illumination, the photocatalytic characteristics of Cu₂S@ZnO heterojunctions with different loading amounts of Cu₂S QDs are evaluated by the corresponding photocatalytic degradation of rhodamine B (RhB) aqueous solution. The results elaborate that the optimized samples (S3 serial specimens with six cycles of SILAR reaction) by means of tailored the band diagram exhibit appreciable improvement of photocatalytic activities among all synthesized samples, attributing to the sensitization of a proper amount of Cu₂S QDs. Such developed architecture not only could form p⁻n junctions with ZnO nanoneedles to facilitate the separation of photo-generated carries but also interact with the surface defects of ZnO NNs to reduce the electron and hole recombination probability. Moreover, the existence of Cu₂S QDs could also extend the light absorption to improve the utilization rate of sunlight. Importantly, under UV light S3 samples demonstrate the remarkably enhanced RhB degradation efficiency, which is clearly testified upon the charge transfer mechanism discussions and evaluations in the present work. Further supplementary investigations illustrate that the developed nanoscale Cu₂S@ZnO heterostructures also possess an excellent photo-stability during our extensive recycling photocatalytic experiments, promising for a wide range of highly efficient and sustainably recyclable photocatalysts applications.

Influence of formulation of ZnO nanoblokes containing metallic ions dopants on their cytotoxicity and protective factors: An in vitro study on human skin cells exposed to UVA radiation

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The [Zn(O)/M] (M = Mg, Al, Ca, Ti) synthesize by thermal method and characterize.

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The metal dopants percolate into crystal lattice of ZnO and stable it.

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The [Zn(O)/M] shows very low amount of Zn⁺² release into culture medium.

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Intracellular reactive oxygen species generation decrease under UVA radiation.

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The [Zn(O)/M] protects of human skin cells against UVA radiation.

Application of ZnO nanoparticles in sunscreens exposes human skin with their adverse effects, which correlates to dissolution/translocation of free Zn⁺² ions. The possibility of decreasing solubility and therefore, reducing toxicity, by structural modifications have been discussed as a solution. The present investigation has developed new metallic lattices of ZnO to reduce cytotoxicity of ZnO nanoparticles. Novel metal-promoted Zn-based nanocomposites ([Zn(O)/M], M = Mg, Al, Ca, Ti) were synthesized and their physicochemical properties and their cytotoxicity were evaluated. Solubility and release studies showed that modification of ZnO structure decreases release of Zn⁺² into culture medium. XRD and UV absorbance analyses showed that metallic-dopants percolate into crystalline lattice of ZnO. This phenomenon is basic reason for stability of Zn-based network. Cell culture studies and MTT assay on human skin cells (HFF-1) exposed to UVA radiation showed that the level of protection of [Zn(O)/M] compounds were more than of [ZnO]. Dichlorofluoroscein diacetate-ROS assay and Zn⁺² release experiments indicated that [Zn(O)/M] nanocomposites decreased the level of ROS generation and Zn⁺² release in compared to ZnO, indicating higher safety of nanocomposites. This study shows that the synthesized Zn-based nanocomposites have potential to be used as safer and more effective sunscreens than ZnO.

Mechanism study on the sulfidation of ZnO with sulfur and iron oxide at high temperature

The mechanism of ZnO sulfidation with sulfur and iron oxide at high temperatures was studied. The thermodynamic analysis, sulfidation behavior of zinc, phase transformations, morphology changes, and surface properties were investigated by HSC 5.0 combined with FactSage 7.0, ICP, XRD, optical microscopy coupled with SEM-EDS, and XPS. The results indicate that increasing temperature and adding iron oxide can not only improve the sulfidation of ZnO but also promote the formation and growth of ZnS crystals. Fe₂O₃ captured the sulfur in the initial sulfidation process as iron sulfides, which then acted as the sulfurizing agent in the late period, thus reducing sulfur escape at high temperatures. The addition of carbon can not only enhance the sulfidation but increase sulfur utilization rate and eliminate the generation of SO₂. The surfaces of marmatite and synthetic zinc sulfides contain high oxygen due to oxidation and oxygen adsorption. Hydroxyl easily absorbs on the surface of iron-bearing zinc sulfide (Zn_1−xFe_xS). The oxidation of synthetic Zn_1−xFe_xS is easier than marmatite in air.

Low temperature synthesis of graphene hybridized surface defective hierarchical core–shell structured ZnO hollow microspheres with long-term stable and enhanced photoelectrochemical activity

Time dependent structural change (solid → core–shell → hollow) of in situ formed ZnO–graphene (ZG) microspheres by low temperature solution process and their photoelectrochemical stability.

Sol–gel based simonkolleite nanopetals with SnO2 nanoparticles in graphite-like amorphous carbon as an efficient and reusable photocatalyst

Sol–gel based simonkolleite nanopetals/SnO₂ nanoparticles embedded in graphite-like amorphous carbon is described as a photocatalyst towards degradation of rhodamine 6G dye under UV illumination.

Enhanced antibacterial activity of Cr doped ZnO nanorods synthesized using microwave processing

Light induced generation of reactive oxygen species from ZnO and Cr:ZnO nanoparticles.

Ag/Cu co-doped ZnS–In2S3 solid solutions: facile synthesis, theoretical calculations and enhanced photocatalytic activity

ZnS–In₂S₃ nanospheres were prepared by a simple hydrothermal method without using any organic solvents or templates.

Defect mediated highly enhanced ultraviolet emission in P-doped ZnO nanorods

The enhancement in UVPL in hydrothermally grown P-doped ZnO is due to the formation of shallow acceptor P_Zn–2V_Zn complex defects.

Synthesis, characterization and cytotoxicity of europium incorporated ZnO–graphene nanocomposites on human MCF7 breast cancer cells

Eu incorporated ZnO–graphene nanocomposite in human breast cancer cells (MCF7) under a confocal laser scanning microscope.