Green Synthesis of Ceria Nanoparticles from Cassava Tubers for Electrochemical Aptasensor Detection of SARS-CoV-2 on a Screen-Printed Carbon Electrode.

Green synthesis approaches for making nanosized ceria using starch from cassava as template molecules to control the particle size are reported. The results of the green synthesis of ceria with an optimum calcination temperature of 800 °C shows a size distribution of each particle of less than 30 nm with an average size of 9.68 nm, while the ratio of Ce3+ to Ce4+ was 25.6%. The green-synthesized nanoceria are applied to increase the sensitivity and attach biomolecules to the electrode surface of the electrochemical aptasensor system for coronavirus disease (COVID-19). The response of the aptasensor to the receptor binding domain of the virus was determined with the potassium ferricyanide redox system. The screen-printed carbon electrode that has been modified with green-synthesized nanoceria shows 1.43 times higher conductivity than the bare electrode, while those modified with commercial ceria increase only 1.18 times. Using an optimized parameter for preparing the aptasensors, the detection and quantification limits were 1.94 and 5.87 ng·mL-1, and the accuracy and precision values were 98.5 and 89.1%. These results show that green-synthesized ceria could be a promising approach for fabricating an electrochemical aptasensor.

Biological Renewable Cellulose-Templated Zn1-XCuXO/Ag2O Nanocomposite Photocatalysts for the Degradation of Methylene Blue.

Herein, Cellulose-templated Zn1-XCuXO/Ag2O nanocomposites were prepared using biological renewable cellulose extracted from water hyacinth (Eichhornia crassipes). Cellulose-templated Cu-doped ZnO catalysts with different amounts of Cu as the dopants (1, 2, 3, and 4%) were prepared and denoted CZ-1, CZ-2, CZ-3, and CZ-4, respectively, for simplicity. The prepared catalysts were tested for the degradation of methylene blue (MB), and 2% Cu-doped ZnO (CZ-2) showed the best catalytic performance (82%), while the pure ZnO, CZ-1, CZ-3, and CZ-4 catalysts exhibited MB dye degradation efficiencies of 54, 63, 65, and 60%, respectively. The best catalyst (CZ-2) was chosen to further improve the degradation efficiency. Different amounts of AgNO3 (10, 15, 30, and 45 mg) were used for the deposition of Ag2O on the surface of CZ-2 and denoted CZA-10, CZA-15, CZA-30, and CZA-45, respectively. Among the composite catalysts, CZA-15 showed remarkable degradation efficiency and degraded 94% of MB, while the CZA-10, CZA-30, and CZA-45 catalysts showed 90, 81, and 79% degradation efficiencies, respectively, under visible light within 100 min of irradiation. The enhanced catalytic performance could be due to the smaller particle size, the higher electron and hole separation and charge transfer efficiencies, and the lower agglomeration in the composite catalyst system. The results also demonstrated that the Cu-doped ZnO prepared with cellulose as a template, followed by the optimum amount of Ag2O deposition, could have promising applications in the degradation of organic pollutants.

Photocatalytic activity of the biogenic mediated green synthesized CuO nanoparticles confined into MgAl LDH matrix.

The global concern over water pollution caused by organic pollutants such as methylene blue (MB) and other dyes has reached a critical level. Herein, the Allium cepa L. peel extract was utilized to fabricate copper oxide (CuO) nanoparticles. The CuO was combined with MgAl-layered double hydroxides (MgAl-LDHs) via a co-precipitation method with varying weight ratios of the CuO/LDHs. The composite catalysts were characterized and tested for the degradation of MB dye. The CuO/MgAl-LDH (1:2) showed the highest photocatalytic performance and achieved 99.20% MB degradation. However, only 90.03, 85.30, 71.87, and 35.53% MB dye was degraded with CuO/MgAl-LDHs (1:1), CuO/MgAl-LDHs (2:1), CuO, and MgAl-LDHs catalysts, respectively. Furthermore, a pseudo-first-order rate constant of the CuO/MgAl-LDHs (1:2) was 0.03141 min-1 while the rate constants for CuO and MgAl-LDHs were 0.0156 and 0.0052 min-1, respectively. The results demonstrated that the composite catalysts exhibited an improved catalytic performance than the pristine CuO and MgAl-LDHs. The higher photocatalytic performances of composite catalysts may be due to the uniform distribution of CuO nanoparticles into the LDH matrix, the higher surface area, and the lower electron and hole recombination rates. Therefore, the CuO/MgAl-LDHs composite catalyst can be one of the candidates used in environmental remediation.

g-C3N4-Co3O4 Z-Scheme Junction with Green-Synthesized ZnO Photocatalyst for Efficient Degradation of Methylene Blue in Aqueous Solution.

A simple wet chemical ultrasonic-assisted synthesis method was employed to prepare visible light-driven g-C3N4-ZnO-Co3O4 (GZC) heterojunction photocatalysts. X-ray diffraction (XRD), scanning electromicroscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), ultraviolet (UV), and electrochemical impedance spectroscopy (EIS) are used to characterize the prepared catalysts. XRD confirms the homogenous phase formation of g-C3N4, ZnO, and Co3O4, and the heterogeneous phase for the composites. The synthesized ZnO and Co3O4 by using cellulose as a template show a rod-like morphology. The specific surface area of the catalytic samples increases due to the cellulose template. The measurements of the energy band gap of a g-C3N4-ZnO-Co3O4 composite showed red-shifted optical absorption to the visible range. The photoluminescence (PL) intensity decreases due to the formation of heterojunction. The PL quenching and EIS result shows that the reduction of the recombination rate and interfacial resistance result in charge carrier kinetic improvement in the catalyst. The photocatalytic performance in the degradation of MB dye of the GZC-3 composite was about 8.2-, 3.3-, and 2.5-fold more than that of the g-C3N4, g-C3N4-ZnO, and g-C3N4-Co3O4 samples. The Mott-Schottky plots of the flat band edge position of g-C3N4, ZnO, Co3O4, and Z-scheme g-C3N4-ZnO-Co3O4 photocatalysts may be created. Based on the stability experiment, GZC-3 shows greater photocatalytic activity after four recycling cycles. As a result, the GZC composite is environmentally friendly and efficient photocatalyst and has the potential to consider in the treatment of dye-contaminated wastewater.

Single-Step Synthesis of Fe-Doped Ni3S2/FeS2 Nanocomposites for Highly Efficient Oxygen Evolution Reaction.

Due to the sluggish kinetic reaction, the electrolytic oxygen evolution reaction (OER) is one of the obstacles in driving overall water splitting for green hydrogen production. In this study, we demonstrate a strategy to improve the OER performance of Ni3S2. The effect of addition of different FeCl2 contents during the hydrothermal process on the OER activity is systematically evaluated. We found that all samples upon the addition of FeCl2 produced Fe-doped Ni3S2 and FeS2 to form a nanocomposite. Their OER performances strongly depend on the amount of FeCl2, where the NSF-0.25 catalyst with 0.25 mmol FeCl2 added during the hydrothermal synthesis shows the best OER performance. Its overpotential was 230 mV versus RHE and it achieves a high current density of 100 mA·cm-2, which was much lower than that of pristine Ni3S2 (320 mV) or RuO2 (370 mV) as the benchmark OER catalyst. The postcharacterizations reveal that NSF-0.25 has gone through an in situ phase transformation into an Fe-NiOOH phase during the OER test. This study presents a simple method and a low-cost material to improve the OER performance with in situ formation of oxyhydroxide.

Biogenic Synthesis of Cu-Doped ZnO Photocatalyst for the Removal of Organic Dye.

The Cu-doped ZnO photocatalysts were prepared with a green and coprecipitation approach by using water hyacinth (Eichhornia crassipes) aquatic plant extract. In the preparation process, different amount of copper precursors such as 1, 2, 3, 4, and 5% of molar ratio were added to zinc nitrate precursors and abbreviated as Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (3%), Cu-ZnO (4%), and Cu-ZnO (5%), respectively. The characterization of the obtained samples was carried out, and the removal of the methylene blue (MB) dye was examined. Out of all catalysts, Cu-ZnO (3%) had the best photocatalytic performance and 89% of the MB dye was degraded. However, the degradation performances of blank (without catalysts), ZnO, Cu-ZnO (1%), Cu-ZnO (2%), Cu-ZnO (4%), and Cu-ZnO (5%) catalysts were 6, 54, 69, 83, 80, and 73%, respectively. Therefore, the use of water hyacinth plant extract with the optimum amount of Cu added to ZnO during the preparation of the catalyst could have a promising application in the degradation of organic pollutants.

Visible light-driven photocatalytic activity of Cu2O/ZnO/Kaolinite-based composite catalyst for the degradation of organic pollutant.

Herein, we design to synthesize a novel Cu2O/ZnO/kaolinite composite catalyst by co-precipitation method. The synthesized composite catalysts were labeled as 5CZK, 10CZK, 15CZK, and 20CZK which represent 5, 10, 15, and 20% of Cu2O, respectively, on ZnO/kaolinite. The photocatalyst samples were characterized with different instruments. Moreover, the methylene blue (MB) dye was used as a target organic pollutant and the degradation was evaluated under visible light irradiation. The highest performance for the degradation of MB was achieved by 10CZK catalyst and degrades 93% within 105 min. However, ZnO (Z), Cu2O/ZnO (CZ), 5CZK, 15CZK, and 20CZK composite catalysts, degrades 28, 66, 76, 71, and 68% of MB dye, respectively. The enhanced degradation efficiency of 10CZK composites catalyst could be due to the higher adsorption properties from metakaolinite and the light-responsive properties of the Cu2O/ZnO samples under visible light. Hence, the resulting composite catalyst could be applicable for environmental remediation.

Self-Protonated Ho-Doped Zn(O,S) as a Green Chemical-Conversion Catalyst to Hydrogenate Nitro to Amino Compounds.

Zn(O,S) has been successfully doped with different amounts of Ho and characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and transient photocurrent (TPC). The as-prepared Ho-doped Zn(O,S) catalysts with different Ho amounts are evaluated for hydrogen evolution reaction. The catalyst with the best performance in evolving hydrogen is further utilized to hydrogenate 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). It is found that doping with Ho obviously enhanced charge transfer and photoresponse properties of the catalyst. Therefore, the modified Zn(O,S) can optimally evolve hydrogen by 18 624 µmol/g, which is 20% higher than that of pristine Zn(O,S). Subsequently, the in situ generated hydrogen ions on catalyst surfaces also play an important role as a hydrogen source to hydrogenate 4-NP to 4-AP without any reducing agents such as NaBH4, which is commonly used as a hydrogen source. As Ho is doped in the lattices of Zn(O,S), it acts not only to separate photocarriers and to enhance the charge transfer but also to shorten the diffusion time of nitrophenolate ions to catalyst surfaces for further photocatalytic hydrogenation reaction (PHR) process. A plausible PHR mechanism has been provided to elucidate the great performance of Ho-modified Zn(O,S) for photocatalytic hydrogenation.

Ag-Decorated MoSx Laminar-Film Electrocatalyst Made with Simple and Scalable Magnetron Sputtering Technique for Hydrogen Evolution: A Defect Model to Explain the Enhanced Electron Transport.

The active edge site, surface defect, and noble-metal nanoparticle have been engineered to improve the electrocatalytic activity of earth-abundant and layered MoS2, but there was no single and facile process to achieve all yet. Here, basal-plane-defected Ag/MoSx lamellae with different Ag contents were deposited by one-step, single-cermet target (ceramic + metal) magnetron sputtering for the electrocatalytic hydrogen evolution reaction (HER). Ag/MoSx (10 vol %) showed a current density of 10 mA/cm2 at an overpotential of 120 mV with a Tafel slope of 42 mV/dec in a 0.5 M H2SO4 solution. The HER performance of Ag-MoSx lamellae was higher than that of the Ag-free one due to the activated basal antisite defects and the decorated Ag for enhancing electron transport. The green magnetron sputtering technique together with the target design has achieved Ag/MoSx lamellae with the film grown using the advantages of active edge-up lamella, S vacancy-type basal sites, and electron transport-enhanced Ag interconnect for enhancing hydrogen evolution.

Effects of Tin in La-Sn-Codoped Zn(O,S) Photocatalyst to Strongly Cleave the Azo Bond in Azobenzene with in Situ Generated Hydrogen.

La-Sn-codoped Zn(O,S) catalysts were synthesized with different amounts (0%, 2.5%, 5%, and 10%) of Sn and a constant amount (10%) of La to improve the photocatalytic hydrogenation reaction (PHR) of azobenzene to aniline. The as-prepared catalysts were carefully characterized and tested for a hydrogenation reaction. The incorporation of Sn significantly enhanced the PHR activities since the incorporated Sn in the Zn(O,S) lattices could increase the conductivity of the catalysts to improve the charge transfer during the catalytic reaction as indicated with EIS measurement. Further measurement with a photoresponse of La-Sn-codoped Zn(O,S) catalysts also exhibited relatively higher intensities as compared to those of La-doped Zn(O,S) and Sn-doped Zn(O,S) catalysts. On the basis of the measurement results of EIS and transient photo current, the La-Sn-codoped Zn(O,S) with the best properties was further utilized for PHR to convert azobenzene to aniline. GC-MS measurement confirmed that 15 ppm azobenzene could be totally converted to aniline in only 60 min which was achieved with a catalyst that was prepared with 5%-Sn and 10%-La doping. The relatively short reaction time indicated that the as-prepared catalyst had a strong reduction capability able to cleave the strong bonding of N═N in azobenzene. The reaction kinetic of the N═N bond cleavage was elucidated based on solvation, adsorption, pinning, and photocatalytic hydrogenation processes on the catalyst surfaces.

Concept of Stagnant Capillarity Water in the Nanoporous SiO2@(Zn,Ni)(O,S) Nanocomposite Photocatalyst as a Strategy to Improve Hydrogen Evolution.

(Zn,Ni)(O,S) nanoparticles were uniformly deposited on nanoporous SiO2 spheres to form SiO2@(Zn,Ni)(O,S) nanocomposites (NCs). To obtain optimum deposition of (Zn,Ni)(O,S) on the SiO2 spheres for the hydrogen evolution reaction (HER), different amounts of 0.25, 0.5, 1, and 1.5 mmol zinc precursor for (Zn,Ni)(O,S) were deposited on SiO2 to obtain different SiO2@(Zn,Ni)(O,S) NCs. All the as-prepared catalysts were examined with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, photocurrent response, photoluminescence spectral studies. Finally, the HER performance was evaluated with SiO2@(Zn,Ni)(O,S). The best SiO2@(Zn,Ni)(O,S)-0.5 surprisingly reached 41.1 mmol/gh for generating H2, which was about a 840% increase as compared to that of the SiO2 sphere-free one. The great improvement in the HER rate was due to the utilization of nanoporous SiO2 spheres. The concept of stagnant capillarity water, adopted from the leaf vein system, was applied to explain the enhanced HER reaction.

Facile synthesis of bimetallic (In,Ga)2(O,S)3 oxy-sulfide nanoflower and its enhanced photocatalytic activity for reduction of Cr(VI).

Hexavalent chromium is one of the most chronic and harmful to human beings, animals, and environmental well-being, and hence needs a high attention to detoxify it. For this purpose, bimetallic (In,Ga)2(O,S)3 oxy-sulfide nanoflower catalyst with different Ga contents was successfully synthesized at a low temperature of 150 °C via a facile method. It was systematically characterized and the visible light-driven photocatalytic reduction of toxic Cr(VI) was 100% completed at 4 min. The Cr(VI) reduction reaction rate constant was 13.8 fold higher than that of Ga-free In2(O,S)3 catalyst. It also showed lower recombination of photogenerated charge carriers, faster interfacial reaction rate, and higher electrical conductivity. The photoexcited electrons and H+ ions played crucial roles in the reduction of Cr(VI). The Cr(III) composition was 12.0% of the total atomic composition. The as-synthesized catalyst showed a tremendously fast Cr(VI) reduction activity and hence, it is promising for detoxification of hazardous Cr(VI).