Superior dye degradation using SnO2-ZnO hybrid heterostructure catalysts

Influence of the Al-Doped ZnO Sputter-Deposition Temperature on Cu(In,Ga)Se2 Solar Cell Performance

Heterojunction Cu(In,Ga)Se₂ (CIGS) solar cells comprise a substrate/Mo/CIGS/CdS/i-ZnO/ZnO:Al. Here, Al-doped zinc oxide (AZO) films were deposited by magnetron sputtering, and the substrate temperature was optimized for CIGS solar cells with two types of CIGS light absorbers with different material properties fabricated by three-stage co-evaporation and two-step metallization followed by sulfurization after selenization (SAS). The microstructure and optoelectronic properties of the AZO thin films fabricated at different substrate temperatures (150-550 °C) were analyzed along with their effects on the CIGS solar cell performance. X-ray diffraction results confirmed that all the deposited AZO films have a hexagonal wurtzite crystal structure regardless of substrate temperature. The optical and electrical properties of the AZO films improved significantly with increasing substrate temperature. Photovoltaic performances of the two types of CIGS solar cells were influenced by changes in the AZO substrate temperature. For the three-stage co-evaporated CIGS cell, as the sputter-deposition temperature of the AZO layer was raised from 150 °C to 550 °C, the efficiencies of CIGS devices decreased monotonically, which suggests the optimum AZO deposition temperature is 150 °C. In contrast, the cell efficiency of CIGS devices fabricated using the two-step SAS-processed CIGS absorbers improved with increasing the AZO deposition temperature from 150 to 350 °C. However, the rise in AZO deposition temperature to 550 °C decreased the cell efficiency, indicating that the optimum AZO deposition temperature was 350 °C. The findings of this study provide insights for the efficient fabrication of CIGS solar cells considering the correlation between CIGS absorber characteristics and AZO layer deposition temperature.

Recent advances in biodecolorization and biodegradation of environmental threatening textile finishing dyes

Organic nature of dyes and their commercially made products are widely utilized in many industries including paper, cosmetics, pharmaceuticals, photography, petroleum as well as in textile manufacturing. The textile industry being the top most consumer of a large variety of dyes during various unit processes operation generates substantial amount of wastewater; hence, nominated as "Major Polluter of Potable Water". The direct discharge of such effluents into environment poses serious threats to the functioning of biotic communities of natural ecosystems. The detection of these synthetic dyes is considered as relatively easy, however, it is extremely difficult to completely eliminate them from wastewater and freshwater ecosystems. Aromatic chemical structure seems to be the main reason behind low biodegradability of these dyes. Currently, various physiochemical and biological methods are employed for their remediation. Among them, microbial degradation has attracted greater attention due to its sustainability, high efficiency, cost effectiveness, and eco-friendly nature. The current review presents recent advances in biodegradation of industrial dyes towards a sustainable and tangible technological innovative solutions as an alternative to existing conventional physicochemical treatment processes.

Electrospun Ag-decorated reduced GO-graft-chitosan composite nanofibers with visible light photocatalytic activity for antibacterial performance

The treatment of water contaminated by bacteria is becoming a necessity. The nanomaterials possessing both intrinsic antibacterial properties and photocatalytic activity are excellent candidates for water disinfection. The powdered form of nanomaterials can be aggregated while embedding the nanomaterials into the NFs can overcome the limitation and enhance the photocatalytic activity and transition from UV-light to visiblelight. Here, graphene oxide (GO) was synthesized, grafted to chitosan, and decorated with silver nanoparticles (Ag NPs) to produce Ag-decorated reduced GO-graft-Chitosan (AGC) NPs. The blends of polyacrylonitrile (PAN) and AGC NPs were prepared in various concentrations of 0.5 wt%, 1.0 wt%, 5.0 wt%, and 10.0 wt% and used to fabricate the electrospun composite NFs. FTIR/ATR, UV-Vis, Raman, XRD, and SEM/EDAX analyses confirmed the successful preparation of the NPs and NFs. The cytotoxicity and antibacterial activity of the composite NFs were received in the order of composite NFs 10.0 wt%˃ 5.0 wt%˃ 1.0 wt%˃ 0.5 wt% in both conditions with/without light irradiation. Their cytotoxicity and antibacterial activity were more under light irradiation compared to the dark. The composite NFs (5.0 wt%) were distinguished as the optimum NFs with cell viability of 80% within 24 h and 60% within 48 h on L929 cells and inhibition zone diameter (IZD) of 12 mm for E. coli and 13 mm for S. aureus after 24 h under the light irradiation. The optimum composite NFs showed thermal stability up to 180 °C and tensile strength of 1.11 MPa with 21.71% elongation at break.

Biosynthesized Bimetallic (ZnOSnO2) Nanoparticles for Photocatalytic Degradation of Organic Dyes and Pharmaceutical Pollutants

The quest for eco-friendly synthetic routes that can be used for the development of multifunctional materials, in particular for water treatment, has reinforced the use of plant extracts as replacement solvents. In this study, bimetallic ZnOSnO2 nanoparticles of different ratios were synthesized using the Sutherlandia frutescens (S. frutescens) plant and tested for the degradation of methylene blue dye and the antibiotics sulfisoxazole and sulfamethoxazole. From the analysis, FTIR confirmed the formation of bimetallic nanoparticles in all ratios within the fingerprint region. SEM revealed homogenous and heterostructures of tubular and spherical structures, with the size distribution ranging from 5–60 nm, respectively. XRD confirmed the formation and the crystallinity of the bimetallic nanoparticles, UV-Vis confirmed the optical properties of the materials and the bandgap values were found between 3.08 and 3.3 eV. From the surface area analysis, type III isotherm and mesoporous structures were confirmed. The photocatalytic activity of these ratios was investigated against MB dye and the antibiotics SSX and SMX. The highest degradation of 88% for MB was obtained using the 50:50 loading ratio at 150 min with a fast kinetic rate of 0.0008 min−1. Furthermore, the holes were the species found to be responsible for the degradation of MB. The SSX and SMX antibiotics exhibited a 66% and 70% degradation, respectively. From this analysis, it can be noted that it is possible to synthesize environmentally safe materials that can be used to degrade various pollutants in our water streams.

Thermally induced oxygen related defects in eco-friendly ZnFe2O4 nanoparticles for enhanced wastewater treatment efficiencies

Herein, a simple but highly effective strategy of thermal annealing to modulate oxygen vacancies related defects in ZnFe₂O₄ (ZFO) nanoparticles for obtaining enhanced wastewater treatment efficiencies is reported. The as-prepared nanoparticles were thermally annealed at three different temperatures (500 °C, 600 °C and 700 °C) and their phase purity was confirmed by X-ray diffraction (XRD). All samples were found to exhibit pure phases of ZFO with different crystallite sizes ranging from 10 nm to 25 nm. The transmission electron microscope (TEM) images showed well dispersed nanoparticles and a strong correlation of grain size growth with annealing temperature was established. The optical absorption and emission characteristics were estimated through UV-visible and Photoluminescence (PL) spectroscopy. Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS) confirmed the variation of oxygen vacancies in the synthesized samples' lattice. The photocatalytic activities of all samples were investigated and the highest efficiencies were recorded for the ZFO samples annealed at 500 °C. Under high salinity condition, the organic dye degradation efficiency of the same sample remained the highest among all. The excellent dye degradation abilities in ZFO samples can be attributed to the abundance of oxygen vacancies in the crystal lattice that slow down the recombination rate during the photocatalysis process. Moreover, cytotoxicity tests revealed that all prepared ZFO samples showed insignificant cell structure effects on Picochlorum sp microalgae, as verified by Fourier-transform infrared (FTIR) spectroscopy. On the other hand, no significant changes were detected on the viable cell concentration and Chlorophyll a content. This work presents a systematic way to finely tune the crystal sizes and to modulate oxygen related defects in ZFO through a highly effective annealing approach to signify their potential in industrial wastewater and seawater treatment processes.

Couple of graphene oxide and functionalized carbon nanotubes for dye degradation enhancement of anatase under visible light and solar irradiation

Graphene oxide sheets (GO) were coupled with carbon nanotubes (CNTs) to enhance the photoactivity of anatase under visible and solar irradiation. The carbon nanotube surface was functionalized in the acidic reflux condition before coupling with GO and decoration of anatase by the sol-gel method. A modified kinetic model was appropriately applied to predict the breakthrough in the methylene blue degradation yield and determine the constant rate which was clearly affected by coupling architecture. The nanocomposite fabricated by the same proportions of GO and CNTs, 3.33%, exhibited the maximal degradation yield, 96.5%, in the dye solution with the initial concentration of 3.0 mg l-1. The characterizations based on X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) revealed that the functionalized CNTs could create the appropriate space between the graphene sheets for uniformly interconnection of anatase via oxygen-containing groups onto the material surfaces. This enhancement in the degradation efficiency could be ascribed to the unique architecture, leading to a decrease in bandgap energy, 2.2 eV, which facilitated the electron-hole separation. Besides of breakthrough in the photoreaction rate, the adequate architecture led to an efficient reduction in the content of carbon-based materials. Also, the performance of mentioned nanocomposite under sunlight photons was effectively higher than that under UV irradiation. The hybrid nanocomposite provided a large number of active sites for photoreactions to facilitate the treatment of wastewater under solar irradiation.

A Sm-doped Egeria-densa-like ZnO nanowires@PVDF nanofiber membrane for high-efficiency water clean

A biomimetic Egeria-densa-like hybrid composite nanofiber membrane was fabricated to degrade organic pollutants in water, with PVDF nanofibers as stems to provide support, and ZnO nanowires as leaves to provide active sites. The Sm-doped ZnO nanowires@PVDF nanofiber membranes were characterized by FE-SEM, X-ray photoelectron spectroscopy, Fourier transform infrared, X-ray diffraction, and UV-vis diffuse reflectance spectrometer. Compared with the pure ZnO nanowires@PVDF nanofiber membrane, the Sm-doped membrane showed higher photocatalytic performance. The excellent photocatalytic activity was attributed to the increased specific surface area and the decreased bandgap of ZnO nanowires after Sm doping, which inhibited the recombination rate of electrons and holes and improved the absorption of visible light. We found that the superoxide free radicals (O₂^-) played a critical role in photocatalytic degradation. The Sm-doped ZnO nanowires@PVDF nanofiber membrane exhibited good stability after 5 cycles of RhB degradation. We believe such Sm-doped hybrid membrane can work as an effective photocatalyst for wastewater treatment.

Trimetallic composite nanofibers for antibacterial and photocatalytic dye degradation of mixed dye water

Membrane technology is an advanced approach to making a healthier and cleaner environment. Using such catalytic membrane technology to get clean, usable water by removal of dye impurities as well as pathogenic microbes is the main goal behind the research work. Here, we present the synthesis and efficacy study of polymethyl methacrylate (PMMA)-based Ag/ZnO/TiO2 trimetallic bifunctional nanofibers with antibacterial and photocatalytic activity. The nanofibers have been proven to be effective for the degradation of methylene blue (MB 93.4%), rhodamine B (Rh 34.6%), auramine-O (Au 65.0%) and fuchsin basic (FB 69.8%) dyes individually within 90 min in daylight. The study is further extended in abating a mixture of these dyes from contaminated water using composite nanofibers. Also, in the case of a mixture of these dyes (3 ppm each), nanofibers show dye degradation efficiency (DDE) of 90.9% (MB), 62.4% (Au) and 90.3% (FB and Rh) in 60 min. The role of Ag nanoparticles with a synergic photocatalytic effect on ZnO and TiO2 is also demonstrated. Also, PMMA/ZnO/TiO2 composite fiber membrane in synergy with silver particles shows better antibacterial activity against Gram-negative bacteria E. coli, making PMMA/Ag/ZnO/TiO2 fibers a promising candidate in water purification.

Facile one-pot synthesis of heterostructure SnO2/ZnO photocatalyst for enhanced photocatalytic degradation of organic dye

In this work, heterostructure SnO₂/ZnO nanocomposite photocatalyst was prepared by a straightforward one step polyol method.

Effect of Thioacetamide Concentration on the Preparation of Single-Phase SnS and SnS2 Thin Films for Optoelectronic Applications

Eco-friendly tin sulfide (SnS) thin films were deposited by chemical solution process using varying concentrations of a sulfur precursor (thioacetamide, 0.50–0.75 M). Optimized thioacetamide concentrations of 0.6 and 0.7 M were obtained for the preparation of single-phase SnS and SnS2 films for photovoltaic absorbers and buffers, respectively. The as-deposited SnS and SnS2 thin films were uniform and pinhole-free without any major cracks and satisfactorily adhered to the substrate; they appeared in dark-brown and orange colors, respectively. Thin-film studies (compositional, structural, optical, and electrical) revealed that the as-prepared SnS and SnS2 films were polycrystalline in nature; exhibited orthorhombic and hexagonal crystal structures with (111) and (001) peaks as the preferred orientation; had optimal band gaps of 1.28 and 2.92 eV; and exhibited p- and n-type electrical conductivity, respectively. This study presents a step towards the growth of SnS and SnS2 binary compounds for a clean and economical power source.

Optimization of Intrinsic ZnO Thickness in Cu(In,Ga)Se2-Based Thin Film Solar Cells

The typical structure of high efficiency Cu(InGa)Se₂ (CIGS)-based thin film solar cells is substrate/Mo/CIGS/CdS/i-ZnO/ZnO:Al(AZO) where the sun light comes through the transparent conducting oxide (i.e., i-ZnO/AZO) side. In this study, the thickness of an intrinsic zinc oxide (i-ZnO) layer was optimized by considering the surface roughness of CIGS light absorbers. The i-ZnO layers with different thicknesses from 30 to 170 nm were deposited via sputtering. The optical properties, microstructures, and morphologies of the i-ZnO thin films with different thicknesses were characterized, and their effects on the CIGS solar cell device properties were explored. Two types of CIGS absorbers prepared by three-stage co-evaporation and two-step sulfurization after the selenization (SAS) processes showed a difference in the preferred crystal orientation, morphology, and surface roughness. During the subsequent post-processing for the fabrication of the glass/Mo/CIGS/CdS/i-ZnO/AZO device, the change in the i-ZnO thickness influenced the performance of the CIGS devices. For the three-stage co-evaporated CIGS cell, the increase in the thickness of the i-ZnO layer from 30 to 90 nm improved the shunt resistance (R_SH), open circuit voltage, and fill factor (FF), as well as the conversion efficiency (10.1% to 11.8%). A further increas of the i-ZnO thickness to 170 nm, deteriorated the device performance parameters, which suggests that 90 nm is close to the optimum thickness of i-ZnO. Conversely, the device with a two-step SAS processed CIGS absorber showed smaller values of the overall R_SH (130-371 Ω cm²) than that of the device with a three-stage co-evaporated CIGS absorber (530-1127 Ω cm²) ranging from 30 nm to 170 nm of i-ZnO thickness. Therefore, the value of the shunt resistance was monotonically increased with the i-ZnO thickness ranging from 30 to 170 nm, which improved the FF and conversion efficiency (6.96% to 8.87%).