Expression of concern: Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO.

Expression of Concern for 'Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO' by Reda S. Salama et al., RSC Adv., 2021, 11, 4318-4326, https://doi.org/10.1039/D0RA09970H.

A comparative study of α-Ni(OH)2 and Ni nanoparticle supported ZIF-8@reduced graphene oxide-derived nitrogen doped carbon for electrocatalytic ethanol oxidation.

Ethanol electrooxidation is an important reaction for fuel cells, however, the major obstacle to ethanol electrocatalysis is the splitting of the carbon-carbon bond to CO2 at lower overpotentials. Herein, a ZIF-8@graphene oxide-derived highly porous nitrogen-doped carbonaceous platform containing zinc oxide was attained for supporting a non-precious Ni-based catalyst. The support was doped with the disordered α-phase Ni(OH)2 NPs and Ni NPs that are converted to Ni(OH)2 through potential cycling in alkaline media. The Ni-based catalysts exhibit high electroactivity owing to the formation of the NiOOH species which has more unpaired d electrons that can bond with the adsorbed species. From CV curves, the EOR onset potential of the α-Ni(OH)2/ZNC@rGO electrode is strongly shifted to negative potential (Eonset = 0.34 V) with a high current density of 8.3 mA cm-2 relative to Ni/ZNC@rGO. The high catalytic activity is related to the large interlayer spacing of α-Ni(OH)2 which facilitates the ion-solvent intercalation. Besides, the porous structure of the NC and the high conductivity of rGO facilitate the kinetic transport of the reactants and electrons. Finally, the catalyst displays a high stability of 92% after 900 cycles relative to the Ni/ZNC@rGO and commercial Pt/C catalysts. Hence, the fabricated α-Ni(OH)2/ZNC@rGO catalyst could be regarded as a potential catalyst for direct EOR in fuel cells.

Selective Reduction of Multivariate Metal-Organic Frameworks for Advanced Electrocatalytic Cathodes in High Areal Capacity and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur batteries hold great promise as next-generation high-energy-density batteries. However, their performance has been limited by the low cycling stability and sulfur utilization. Herein, we demonstrate that a selective reduction of the multivariate metal-organic framework, MTV-MOF-74 (Co, Ni, Fe), transforms the framework into a porous carbon decorated with bimetallic CoNi alloy and Fe3O4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li2S. Electrochemical studies on coin cells containing 89 wt % sulfur loading revealed a reversible capacity of 1439.8 mA h g-1 at 0.05 C and prolonged cycling stability for 1000 cycles at 1 C/1060.2 mA h g-1 with a decay rate of 0.018% per cycle. At a high areal sulfur loading of 6.9 mg cm-2 and lean electrolyte/sulfur ratio (4.5 µL:1.0 mg), the battery based on the 89S@CoNiFe3O4/PC cathode provides a high areal capacity of 6.7 mA h cm-2. The battery exhibits an outstanding power density of 849 W kg-1 at 5 C and delivers a specific energy of 216 W h kg-1 at 2 C, corresponding to a specific power of 433 W kg-1. Density functional theory shows that the observed results are due to the strong interaction between the CoNi alloy and Fe3O4, facilitated by charge transfer between the polysulfides and the substrate.

Stable polyethylene glycol/biochar composite as a cost-effective photothermal absorber for 24 hours of steam and electricity cogeneration.

Seawater desalination powered by solar energy is the most environmentally and economical solution in responding to the global water and energy crisis. However, solar desalination has been negatively impacted by intermittent sun radiation that alternates between day and night. In this study, sugarcane bagasse (SCB) was recycled via the pyrolysis process to biochar as a cost-effective solar absorber. Besides, polyethylene glycol (PEG) as a phase change material was encapsulated in the abundant pore structure of biochar to store the thermal energy for 24 hours of continuous steam generation. The BDB/1.5 PEG evaporator exhibited an evaporation rate of 2.11 kg m-2 h-1 (98.1% efficiency) under 1 sun irradiation. Additionally, the BDB/1.5 PEG evaporator incorporated by the TEC1-12706 module for continuous steam and electricity generation with a power density of 320.41 mW m-2. Moreover, 10 continuous hours of evaporation were applied to the composite demonstrating outstanding stability. The composite exhibited high water purification efficiency through solar desalination due to the abundant functional groups on the biochar surface. Finally, the resulting low-cost and highly efficient PCM-based absorber can be used on a wide scale to produce fresh water and energy.

Construction of thickness-controllable bimetallic sulfides/reduced graphene oxide as a binder-free positive electrode for hybrid supercapacitors.

Devices for electrochemical energy storage with exceptional capacitance and rate performance, outstanding energy density, simple fabrication, long-term stability, and remarkable reversibility have always been in high demand. Herein, a high-performance binder-free electrode (3D NiCuS/rGO) was fabricated as a supercapacitor by a simple electrodeposition process on a Ni foam (NF) surface. The thickness of the deposited materials on the NF surface was adjusted by applying a low cycle number of cyclic voltammetry (5 cycles) which produced a thin layer and thus enabled the easier penetration of electrolytes to promote electron and charge transfer. The NiCuS was anchored by graphene layers producing nicely integrated materials leading to a higher electroconductivity and a larger surface area electrode. The as-fabricated electrode displayed a high specific capacitance (2211.029 F g-1 at 5 mV s-1). The NiCuS/rGO/NF//active carbon device can achieve a stable voltage window of 1.5 V with a highly specific capacitance of 84.3 F g-1 at a current density of 1 A g-1. At a power density of 749 W kg-1, a satisfactory energy density of 26.3 W h kg-1 was achieved, with outstanding coulombic efficiency of 100% and an admirable life span of 96.2% after 10 000 GCD cycles suggesting the significant potential of the as-prepared materials for practical supercapacitors.

Solar-driven seawater desalination via plasmonic hybrid MOF/polymer and its antibacterial activity.

In recent years, solar seawater desalination has been considered to be a promising and cost-effective technique to produce clean sources for water treatment and water deficiency. In addition, this technique shows high photothermal conversion efficiency by solar collectors to transfer solar energy into heat and the transformation of molecules in the capillaries of solar evaporators. In this study, we report the preparation of graphene-supported MIL-125 with polyurethane foam (MGPU) for solar steam generation. We modified MGPU by using the plasmonic nanoparticles of Ag and a polymer of polyaniline to increase the evaporation rate. Polyurethane foam can float on the surface of water and self-pump water by its hydrophilic porous structure, superior thermal insulation capabilities, and easy fabrication. MIL-125 has a high salt rejection and higher water permeability. It can reduce the affinity between water molecules and the pore surface of membrane, making it simple for water molecules to move through the pores. GO is a great alternative for steam generation applications since it exhibits broad-band light. The strong solar absorption, photothermal conversion efficiency, and photoreaction efficiency are enhanced by the use of silver nanoparticles in the photoreaction. The salt resistance capability is enhanced in saline water in the presence of polyaniline in a composite. Under one solar irradiation, the Ag/PANI/GO@MIL-125 (Ag-PMG) nanocomposite demonstrates an average 1.26 kg m2 h-1 rate of evaporation and an efficiency as high as 90%. The composite exhibits remarkable stability and durability after more than 10 cycles of use without a noticeable decrease in activity. In addition, the composite exhibits excellent organic dye removal from contaminated water and generates pure condensed freshwater. The antibacterial photoactivity of the photocatalysts was examined against B. subtilis and E. coli. The results demonstrate that Ag-PMG shows higher antibacterial activity than MIL-125 and PMG. It was shown that the presence of rGO, PANI, and Ag in the sample enhances the antimicrobial activity.

Cesium salt of tungstophosphoric acid/mesoporous (zirconia-silica) composite for highly efficient synthesis of 7-hydroxy-4-methyl coumarin and removal of methylene blue.

The removal of harmful organic dyes from aqueous solutions has drawn the attention of scientists because of the substantial threat they pose to society's worldwide health. Hence, it is crucial to design an adsorbent that is both very effective in removing dyes and has the benefit of being inexpensive. In the present work, Cs salts of tungstophosphoric acid (CPW) supported mesoporous Zr-mSiO2 (mZS) with varying extents of Cs ions have been prepared by a two-step impregnation technique. Accordingly, a lowering in the surface acidity modes was observed after Cs exchanged protons of H3W12O40 and formed salts immobilized on the mZS support. After exchanging the protons with Cs ions, the characterization results revealed that the primary Keggin structure was unaltered. Moreover, the Cs exchanged catalysts had higher surface area than the parent H3W12O40/mZS, suggesting that Cs reacts with H3W12O40 molecules to create new primary particles with smaller sizes possessing inter-crystallite centers with a higher dispersion degree. With an increase in Cs content and thus a decrease in the acid strength and surface acid density, the methylene blue (MB) monolayer adsorption capacities on CPW/mZS catalysts were increased and reached an uptake capacity of 359.9 mg g-1 for Cs3PW12O40/mZS (3.0CPW/mZS). The catalytic formation of 7-hydroxy-4-methyl coumarin was also studied at optimum conditions and it is found that the catalytic activity is influenced by the amount of exchangeable Cs with PW on the mZrS support, which is in turn influenced by the catalyst acidity. The catalyst kept approximately the initial catalytic activity even after the fifth cycle.

Silver sulfide decorated carbonaceous sawdust/ES-PANI composites as salt-resistant solar steam generator.

Solar steam generation (SSG) is a potential approach for resolving the global water and energy crisis while causing the least amount of environmental damage. However, using adaptable photothermal absorbers with salt resistance through a simple, scalable, and cost-effective production approach is difficult. Herein, taking advantage of the ultra-fast water transportation in capillaries, and the large seawater storage capacity of wood, we develop a highly efficient natural evaporator. The wood wastes (sawdust) were carbonized at low temperatures to fabricate a green and low-cost carbonaceous porous material (CW). To enhance the salt resistance in high saline water, this evaporator was coated with polyaniline emeraldine salt (ES-PANI) which was synthesized through facile and cost-effective one-step oxidation of aniline. Furthermore, the composite was decorated with silver sulfide to increase the evaporation rate which reached up to 1.1 kg m-2 h-1 under 1 sun irradiation with 91.5% efficiency. Besides, the evaporator performs exceptionally well over 10 cycles due to the salt resistance capability of ES-PANI which generates a "Donnan exclusion" effect against cations in saline water. The Ag2S@PANI/CW evaporator may be a viable large-scale generator of drinking water due to its high efficiency for energy conversion, simple and low-cost fabrication approach, salt-resistance, and durability.

High efficiency solar desalination and dye retention of plasmonic/reduced graphene oxide based copper oxide nanocomposites.

Water desalination via solar-driven interfacial evaporation is one of the most essential technologies to limit the problem of global freshwater scarcity. Searching for a highly efficient, stable, eco-friendly, and cost-effective solar-absorber material that can collect the full solar spectrum is critically important for solar steam generation. This study reports the development of a new solar thermal evaporation system based on plasmonic copper oxide/reduced graphene oxide (rGO). The silver nanoparticles in the composite exhibit a very strong solar absorption. Also, rGO and CuO nanoparticles offer excellent thermal absorptivity. Polyurethane was used as the support and as a thermal insulator. Moreover, filter paper was used for fast water delivery to the surface of the solar absorber. Ag/CuO-rGO nanocomposite is manifested to be one of the most efficient solar-absorbers reported to date for solar desalination which exhibits an average 2.6 kg m-2 h-1 evaporation rate with solar thermal efficiency up to 92.5% under 1 sun irradiation. Furthermore, the composite has excellent stability and durability as it displays stable evaporation rates for more than 10 repeated cycles in use, with no significant decrease in the activity. Besides, the successful removal of various organic dyes from contaminated water is also revealed, resulting in the production of clean condensed freshwater. Finally, this work commences a new avenue of synthesizing cost-effective thermal absorbers based on metal oxides.

Palladium supported on mixed-metal-organic framework (Co-Mn-MOF-74) for efficient catalytic oxidation of CO.

Successful monometallic and bimetallic metal-organic frameworks with different Co/Mn ratios have been synthesized under solvothermal conditions. The as-synthesized MOFs followed by deposition of Pd nanoparticles with 0.5 to 7 wt%. The XRD, BET, SEM, TEM, EDAX and FT-IR characterization results reveal that bimetallic MOFs and Pd nanoparticles were finely dispersed on the prepared MOFs surfaces. XRD results confirm the formation of the desire MOFs and show the high degree of dispersion of Pd nanoparticles. TEM images show that Pd nanoparticles are nano-sized with almost uniform shape. EDAX shows that Pd nanoparticles successfully loaded on Co0.5-Mn0.5-MOF-74 catalyst. CO oxidation as a model reaction was then used to assess the catalytic performance of the prepared catalysts. The catalytic activity results show enhancement in the catalytic activities of monometallic MOFs after introducing another metal in the same framework and show an excellent improvement in CO conversion after loading with Pd nanoparticles. Furthermore, the samples that contain Pd nanoparticles exhibits higher catalytic activities which raised with increasing the content of Pd nanoparticles.

Sulfamic acid incorporated HKUST-1: a highly active catalyst and efficient adsorbent.

Herein we introduce an effective approach for incorporating sulfamic acid (SA) into HKUST-1. The synthesized materials have been characterized using XRD, XPS, BET, FT-IR, SEM, EDX and TEM. The X-ray diffraction pattern of SA@HKUST-1 is analogous to that of parent HKUST-1 in line shape and d-spacing, proving that chemical modification could be obtained without damage to structural solidity. The XPS spectra confirmed successful sulfonation, due to the single S 2p peak being attributable to SO3H groups at 168 eV. Catalytic efficiency was studied for 7-hydroxy-4-methyl coumarin and 3,4-dihydropyrimidinone synthesis and it was found to be highly dependent on the amount of SA loaded over HKUST-1. Moreover, the adsorptive removal activity of some common organic and inorganic pollutants from water has been studied. To fully understand the adsorption process, the effects of initial dye concentration, pH of solution, adsorbent dosage, contact time and temperature on the adsorption process were successfully studied. Under the optimum conditions 10 wt% SA@HKUST-1 was able to reach the maximum adsorption capacity for Pb2+ (298 mg g-1) and Malachite green (290 mg g-1). Hopefully, this will facilitate research on improving the prospective use of MOFs for future applications.

Nano-sized mesoporous phosphated tin oxide as an efficient solid acid catalyst.

Herein, we prepared a mesoporous tin oxide catalyst (mSnO2) activated with phosphate species by the adsorption of phosphate ions from a phosphoric acid solution onto tin oxyhydroxide (Sn(OH)4) surface. The phosphate content ranged from 3 to 45 wt%. The nonaqueous titration of n-butylamine in acetonitrile was used to determine the total surface acidity level. FTIR of chemically adsorbed pyridine was used to differentiate between the Lewis and Brönsted acid sites. Thermal and X-ray diffraction analysis indicated that the addition of phosphate groups stabilized the mesostructure of mSnO2 and enabled it to keep its crystalline size at the nanoscale. FTIR analysis indicated the polymerization of the HPO4 2- groups into P2O7 4-, which in turn reacts with SnO2 to form a SnP2O7 layer, which stabilizes the mesoporous structure of SnO2. The acidity measurements showed that the phosphate species are distributed homogeneously over the mSnO2 surface until surface saturation coverage at 25 wt% PO4 3-, at which point the acid strength and surface acidity level are maximized. The catalytic activity was tested for the synthesis of hydroquinone diacetate, where it was found that the % yield of hydroquinone diacetate compound increased gradually with the increase in PO4 3- loading on mSnO2 until it reached a maximum value of 93.2% for the 25% PO4 3-/mSnO2 catalyst with 100% selectivity and excellent reusability for three consecutive runs with no loss in activity.

Palladium Nanoparticles Supported on Ce-Metal-Organic Framework for Efficient CO Oxidation and Low-Temperature CO2 Capture.

In this article, we report the lowest-temperature CO oxidation catalyst supported on metal-organic frameworks (MOFs). We have developed a facile, general, and effective approach based on microwave irradiation for the incorporation of Pd nanoparticle catalyst within Ce-MOF. The resulting Pd/Ce-MOF material is a unique catalyst that is capable of CO oxidation at modest temperatures and also of efficient uptake of the product CO2 gas at low temperatures. The observed catalytic activity of this material toward CO oxidation is significantly higher than those of other reported metal nanoparticles supported on MOFs. The high activity of the Pd/Ce-MOF catalyst is due to the presence of Ce(III) and Ce(IV) ions within the metal-organic framework support. The Pd nanoparticles supported on the Ce-MOF store oxygen in the form of a thin palladium oxide layer at the particle-support interface, in addition to the oxygen stored on the Ce(III)/Ce(IV) centers. Oxygen from these reservoirs can be released during CO oxidation at 373 K. At lower temperatures (273 K), the Pd/Ce-MOF has a significant CO2 uptake of 3.5 mmol/g.