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.

Photocatalytic H2O2 Generation over Microsphere Carbon-Assisted Hierarchical Indium Sulfide Nanoflakes via a Two-Step One-Electron Pathway.

The increasing demand for an alternative to traditional fuel has motivated intensive research and drawn more attention. H2O2 has emerged as an alternative due to its high capabilities, relatively safer nature as a fuel, and ease of transportation. The photocatalytic method is adopted to generate H2O2 using sustainable light energy to achieve an entire green system for a completely environmentally friendly process. Herein, the synthesized microsphere carbon-assisted hierarchical two-dimensional (2D) indium sulfide (In2S3) nanoflakes have been characterized thoroughly by various techniques such as X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectra (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR). The photocatalytic performance of the In2S3-based photocatalysts can be promoted with the carbon layer assisting in facilitating the transfer of the photogenerated electrons and narrowing their band gaps. Optimized In2S3 successfully yielded 31.2 mM g-1 h-1 in the photocatalytic oxygen reduction reaction (ORR) process. Based on the results of different radical trapping experiments and different reaction conditions, the catalytic ORR process is proposed to be a two-step one-electron pathway.

Highly efficient photocatalytic H2O2 generation over dysprosium oxide-integrated g-C3N4 nanosheets with nitrogen deficiency.

The increasing global crisis considers energy as the fundamental cause to conduct extensive research work to find clean alternative methods with high capabilities such as H2O2 synthesis. Photocatalytic H2O2 production can tackle this growing issue by maintaining environmental remediation. In this work, dysprosium oxide (Dy-oxide)-integrated g-C3N4 has been synthesized and characterized with XRD, SEM, TEM, XPS, EPR, DRS, PL, and electrochemical analyses. Simulated solar light irradiation implemented photocatalytic H2O2 production using the as-prepared catalysts. The facile preparation technique in the Ar atmosphere raises more N deficiency in the g-C3N4 matrix. N-deficient g-C3N4 nanosheets with an exceptionally high photocatalytic performance can be further enhanced by integrating well-dispersed Dysprosium oxide (Dy2O3) particles onto g-C3N4. This study reports bandgap narrowing and various surface defects on g-C3N4 with trace amounts of Dy2O3. Undoped g-C3N4 (Dy0) yielded 20.27 mM⋅g-1⋅h-1, while the optimized photocatalyst Dy15 showed high performance of H2O2 production up to 48.36 mM⋅g-1⋅h-1. It is approximately 2.4 times higher than the pristine g-C3N4. Dy15 proves the positive impact of Dy-oxide on enhancing the N-deficient g-C3N4 performance towards photocatalytic H2O2 production. This work highlights the oxygen reduction reaction (ORR) through a mixed pathway of well-known two-step one-electron and one-step two-electron processes in H2O2 generation.

Solar-light-driven ternary MgO/TiO2/g-C3N4 heterojunction photocatalyst with surface defects for dinitrobenzene pollutant reduction.

Defect engineering and heterojunction are promising strategies to improve the photocatalytic performance of particular catalyst through effective charge carrier separation and transport. Herein, we developed Z-scheme MgO/TiO2/g-C3N4 ternary heterojunction photocatalyst with surface defects and effective charge separation for reduction of recalcitrant dinitrobenzene isomers under simulated solar light irradiation. Mott-Schottky (MS) plot analysis and electron spin resonance (ESR) radical trapping experiment suggested the formation of Z-scheme heterojunction at the interface of TiO2/g-C3N4, which played a crucial role in the electron-hole separation. Incorporating MgO into the structure further enhances charge separation via Ti3+ and oxygen vacancy (OV) defects formation at the TiO2/MgO interface as confirmed by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) analyses. Besides, the surface basicity of MgO enhanced conversion of dinitrobenzene (DNB) isomers through formation of nitrophenylhydroxylamine intermediate which can easily be reduced to phenylenediamines (PDAs). As confirmed by high performance liquid chromatography (HPLC) analysis, excellent selectivity for PDAs (95-98%) was achieved in 90 min with ternary MgO/TiO2/g-C3N4 composite compared to the binary MgO/TiO2 and TiO2/g-C3N4. A possible reaction pathway and photocatalytic reduction mechanism were proposed and elucidated. This work demonstrated an effective strategy to reduce recalcitrant dinitrobenzene isomers using efficient, low-cost, and environmental benign photocatalyst with a facile identification of reaction intermediates.

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.

Synthesis and characterizations of natural limestone-derived nano-hydroxyapatite (HAp): a comparison study of different metals doped HAps on antibacterial activity.

Earth-abundant mineral limestone obtained from North Sumatera, Indonesia, has been utilized to synthesize nano-hydroxyapatite (HAp). Although HAp is biocompatible to the human bone, its antibacterial activity is still very low. Herein, different metal ions (i.e., Ag, Cu, Zn, and Mg) were doped into HAp to improve the antibacterial activity. The as-synthesized HAp was characterized by X-ray ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy disperse spectroscopy (EDS), Fourier transmission infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET). The antibacterial test showed that the performance of HAp to inactivate bacterial growth was significantly improved after incorporating the metal ion dopants into HAp. Ag-HAp exhibited the highest activity toward E. coli and S. aureus with an antibacterial rate of 99.9 ± 0.1%, followed by Zn-HAp, Cu-HAp, and Mg-HAp.

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.

Synthesis and characterization of La-doped Zn(O,S) photocatalyst for green chemical detoxification of 4-nitrophenol.

La-doped Zn(O,S) nanoparticles (NPs) with different contents of lanthanum have been synthesized with a simple sol-gel method at low temperature (90 ℃) for 4-nitrophenol (4-NP) detoxification. The as-prepared catalysts were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), photoluminescence (PL) and UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and photoresponsivity. In this work, it is considered that the detoxification of 4-NP to 4-aminophenol (4-AP) without NaBH4 by using photocatalytic method is a green chemical conversion. The experimental data showed 30 ppm toxic 4-NP had been totally converted to useful 4-aminophenol (4-AP) with lower toxicity in 2 h, which was confirmed with a specific peak shift as indicated with UV-vis absorbance spectra and high performance liquid chromatography (HPLC) measurement. The lower amount of evolved hydrogen from photocatalytic process on La-doped Zn(O,S) NPs in the presence of 4-NP confirmed the produced hydrogen was consumed as a reducing agent during the 4-NP-to-4-AP conversion. The photocatalytic detoxification of 4-NP to 4-AP had been demonstrated and an appropriate mechanism based on the experimental data had been proposed and elucidated in this work.

Abiotic Synthesis with the C-C Bond Formation in Ethanol from CO2 over (Cu,M)(O,S) Catalysts with M = Ni, Sn, and Co.

We demonstrate copper-based (Cu,M)(O,S) oxysulfide catalysts with M = Ni, Sn, and Co for the abiotic chemical synthesis of ethanol (EtOH) with the C-C bond formation by passing carbon dioxide (CO2) through an aqueous dispersion bath at ambient environment. (Cu,Ni)(O,S) with 12.1% anion vacancies had the best EtOH yield, followed by (Cu,Sn)(O,S) and (Cu,Co)(O,S). The ethanol yield with 0.2 g (Cu,Ni)(O,S) catalyst over a span of 20 h achieved 5.2 mg. The ethanol yield is inversely proportional to the amount of anion vacancy. The kinetic mechanism for converting the dissolved CO2 into the C2 oxygenate is proposed. Molecular interaction, pinning, and bond weakening with anion vacancy of highly strained catalyst, the electron hopping at Cu+/Cu2+ sites, and the reaction orientation of hydrocarbon intermediates are the three critical issues in order to make the ambient chemical conversion of inorganic CO2 to organic EtOH with the C-C bond formation in water realized. On the other hand, Cu(O,S) with the highest amount of 22.7% anion vacancies did not produce ethanol due to its strain energy relaxation opposing to the pinning and weakening of O-H and C-O bonds.

CuMnOS Nanoflowers with Different Cu+/Cu2+ Ratios for the CO2-to-CH3OH and the CH3OH-to-H2 Redox Reactions.

A conservative CO2-Methanol (CH3OH) regeneration cycle, to capture and reutilize the greenhouse gas of CO2 by aqueous hydrogenation for industry-useful CH3OH and to convert aqueous CH3OH solution by dehydrogenation for the clean energy of hydrogen (H2), is demonstrated at normal temperature and pressure (NTP) with two kinds of CuMnOS nanoflower catalysts. The [Cu+]-high CuMnOS led to a CH3OH yield of 21.1 mmol·g-1catal.·h-1 in the CuMnOS-CO2-H2O system and the other [Cu+]-low one had a H2 yield of 7.65 mmol·g-1catal.·h-1 in the CuMnOS-CH3OH-H2O system. The successful redox reactions at NTP rely on active lattice oxygen of CuMnOS catalysts and its charge (hole or electron) transfer ability between Cu+ and Cu2+. The CO2-hydrogenated CH3OH in aqueous solution is not only a fuel but also an ideal liquid hydrogen storage system for transportation application.

Facile Synthesis of n-type (AgIn)(x)Zn(2(1-x))S2/p-type Ag2S Nanocomposite for Visible Light Photocatalytic Reduction To Detoxify Hexavalent Chromium.

n-type (AgIn)(x)Zn(2(1-x))S2/p-type Ag2S nanocomposites with 10%, 20%, and 30% Ag2S loading were successfully synthesized via the simple solvothermal and sol gel methods. The as-prepared nanocomposites were characterized, and their visible light photocatalytic reductions were tested for detoxification of hexavalent chromium (Cr(VI)). The results showed only 20 mg of the as-prepared nanocomposites could reduce 100 mL of 20 ppm potassium dichromate by almost 100% in less than 90 min without adding any hole scavenger agents and pH adjustment (pH = 7). The good photocatalytic reduction was related to the narrower bandgap of (AgIn)(x)Zn(2(1-x))S2 solid solution because of the hybridized orbitals of Ag, In, Zn, and S and low recombination rate of photogenerated electron and hole pairs due to the effectiveness of p-type Ag2S and n-type (AgIn)(x)Zn(2(1-x))S2 nanoheterojunctions. This work not only gives a contribution to the creation of visible light photocatalysis for wide-bandgap semiconductors, but also extends our technological viewpoints in designing highly efficient metal sulfide photocatalyst. To the best of our knowledge, this work is the first finding of a high photocatalytic reduction of hexavalent chromium under visible light illumination by simultaneously using both concepts of p-n nanoheterojunction and solid solution in our photocatalyst design. In this present work, these concepts were used to replace the use of hole scavenger agents, which were commonly used by many other works to retard the recombination rate of photoinduced electron and hole pairs for photodegradation of hexavalent chromium.