Whereas noble metal compounds have long been central in catalysis, Earth-abundant metal-based catalysts have in the same time remained undeveloped. Yet the efficacy of Earth-abundant metal catalysts was already shown at the very beginning of the 20th century with the Fe-catalyzed Haber–Bosch process of ammonia synthesis and later in the Fischer–Tropsch reaction. Nanoscience has revolutionized the world of catalysis since it was observed that very small Au nanoparticles (NPs) and other noble metal NPs are extraordinarily efficient. Therefore the development of Earth-abundant metals NPs is more recent, but it has appeared necessary due to their “greenness”. This review highlights catalysis by NPs of Earth-abundant transition metals that include Mn, Fe, Co, Ni, Cu, early transition metals (Ti, V, Cr, Zr, Nb and W) and their nanocomposites with emphasis on basic principles and literature reported during the last 5 years. A very large spectrum of catalytic reactions has been successfully disclosed, and catalysis has been examined for each metal starting with zero-valent metal NPs followed by oxides and other nanocomposites. The last section highlights the catalytic activities of bi- and trimetallic NPs. Indeed this later family is very promising and simultaneously benefits from increased stability, efficiency and selectivity, compared to monometallic NPs, due to synergistic substrate activation.

The recent development of efficient Earth-abundant transition-metal nanocatalysts

Waste to MOFs: sustainable linker, metal, and solvent sources for value-added MOF synthesis and applications

Herein, the synthesis, characterization, and water treatment application of reduced graphene oxide-manganese oxide-black cumin hybrid composite, rGO-MnO2/BC, has been reported. The rGO-MnO2/BC was synthesized by incorporating MnO2 particles into reduced graphene oxide functionalized with functional groups of black cumin seeds. The prepared rGO-MnO2/BC was highly amorphous, having large numbers of functional sites, and was evaluated for adsorptive removal of arsenic and methylene blue from their respective aqueous solutions. Adsorption capacities of rGO-MnO2/BC for methylene blue and arsenite were evaluated in batch manner under optimum conditions. 1.0 g/L dosage of rGO-MnO2/BC could remove approximately 99 % of methylene blue and arsenite from initial concentration of 10.0 and 1.0 mg/L, respectively, after 75 min at 7.0 pH, and 27 °C temperature. The sorption data was evaluated to propose the adsorption mechanism by fitting into isotherm and kinetic models. The process of methylene blue and arsenite sorption was proved to be exothermic and feasible based on thermodynamic parameters. The Freundlich isotherm was most suitable for arsenite sorption and both Langmuir and Freundlich isotherms were suitable for methylene blue sorption data. The sorption kinetics followed pseudo-second order relationship for both adsorbates. The exploration of thermodynamics, isotherms, and kinetics parameters revealed physicochemical sorption mechanisms for both adsorbates onto rGO-MnO2/BC surface. The Langmuir sorption capacity of rGO-MnO2/BC for methylene blue and arsenite were found to be 232.5 and 14.7  mg/g, respectively, at 27 °C. The rGO-MnO2/BC is easy to prepare and is low-cost material, and showed high adsorption capacity as compared to the other reported adsorbents. Therefore, the application of rGO-MnO2/BC will be beneficial for upcoming research on water treatment technologies.

Reduce graphene oxide-manganese oxide-black cumin based hybrid composite (rGO-MnO2/BC): A novel material for water remediation

In this study, quaternary-ammonium-functionalized metal–organic frameworks (MOFs) Et-N-Cu(BDC-NH2)(DMF), were prepared, characterized, and applied for the highly effective removal of metal cyanide complexes, including Pd(CN)42−, Co(CN)63−, and Fe(CN)63−. Batch studies were carried out, and the maximum adsorption capacities of Pd(II), Co(III), and Fe(III) reached 172.9, 101.0, and 102.6, respectively. Adsorption was rapid, and equilibrium was established within 30 min. Et-N-Cu(BDC-NH2)(DMF) exhibited high thermal and chemical stability. Furthermore, absorbed Pd(CN)42− was selectively recovered by two-step elution. First, Co(CN)63− and Fe(CN)63− were eluted with a 1.5 mol L−1 KCl solution. Elution rates of Co(CN)63− and Fe(CN)63− were greater than 98.0%, whereas the elution percentage of Pd(CN)42− was less than 2.0%. Second, >97.0% Pd(CN)42− on the loaded MOFs was eluted using a 2.0 mol L−1 KI solution. The recovery rate of Pd(CN)42− was greater than 91.0% after five testing cycles. Adsorption isotherms, kinetics models, and adsorption thermodynamics of Pd(CN)42− on Et-N-Cu(BDC-NH2) (DMF) were also systematically investigated. The Et-N-Cu(BDC-NH2) (DMF) absorbent exhibited a rapid, excellent ability for the adsorption of metal cyanide complexes.

https://www.mdpi.com/1420-3049/23/8/2086/pdf

Highly Effective Removal of Metal Cyanide Complexes and Recovery of Palladium Using Quaternary-Ammonium-Functionalized MOFs

Two types of hierarchical mesoporous CuS nanospheres, i.e., solid spheres (SSs) and hollow spheres (HSs), were controllably synthesized by a facile and green microwave-assisted wet chemical process, using copper acetate and thiourea aqueous solutions as precursors without a surfactant or template. The crystal structures, morphologies and photocatalytic properties of the products were characterized by various techniques. The results indicated that CuS SSs of 150 ± 50 nm in diameter are made of nanograins of about 10 nm in size, whereas CuS HSs of 400 ± 100 nm in outer-diameter are the assembly of ultrathin nanosheets in thickness of about 6 nm. The as-obtained both CuS architectures exhibit far superior dye degradation properties than commercial CuS powder for the decomposition of organic dyes including rhodamine B, methylene blue and malachite green with the help of hydrogen peroxide under visible light. Specially, using CuS HSs as catalyst, the decoloring rates of three organic dyes catalyst reach above 90% after just 1 min of irradiation and are approaching 100% after 20 min of irradiation, suggesting a fast and efficient photocatalytic activity and a promising application in industrial wastewater purification.

Microwave-assisted controllable synthesis of hierarchical CuS nanospheres displaying fast and efficient photocatalytic activities

Terephthalic acid was recycled from waste PET bottles with a basic hydrolysis technique and characterized with UV and FTIR spectroscopy. Copper-based metal–organic framework Cu(BDC) was synthesized at room temperature without any additive; two different temperatures were chosen to activate the obtained material. Characterization studies were performed using XRD, N2 physisorption, STEM and EDX. The obtained material was tested as a catalyst for the reduction of methyl orange with NaBH4 in aqueous solutions. Thermal activation at 160 °C proved to be mandatory for catalytic activity; although higher temperature activation did not cause significant enhancement. Rapid dye removal was monitored by continuous photometry at λ
 max. The results were quite satisfactory (about 85% removal in 5 min); even higher than the published results for precious metal (i.e., Au, Pt and Ag) nanoparticles. In an increased reaction scale, UV–visible spectra and mass spectrum were recorded to help elucidating the possible reaction mechanism. In addition, recycling experiment were performed in 100-ml scale without any kind of re-activation (washing or drying) to show the ability of Cu(BDC) as a stable catalyst for reductive dye removal (and probably similar reactions as well).

Cu(BDC) as a catalyst for rapid reduction of methyl orange: room temperature synthesis using recycled terephthalic acid

Efficient Synthesis of Some New Chromenopyrimidine Azo- Dyes Catalyzed by Cu/SBA-15

Novel Synthesis of Some 2-Aminochromene Derivatives using Nano-sized Zirconium Oxide as Catalyst

Copper sulfides (covellite, digenite and djurleite) were synthesized using microwave irradiation. Copper acetate and thiourea were chosen as precursors and used at a fixed ratio. Crystalline phase and morphology (particles, spheres and inter-grown belts) were changed by only changing the synthetic media (water, DMF and a 1:1 V/V mixture of them). A domestic microwave oven was used at 1000 watt for only 20 s for each synthesis. The obtained samples were characterized using powder XRD, FESEM, and EDX; results were used to postulate the differences in phase and morphology of the obtained samples. All samples were tested as reduction catalysts for methyl orange degradation by NaBH4 and time-dependent UV–vis spectroscopy was used to compare their activity. PAPER 2017 RECEIVED 1 November 2017 REVISED 27 November 2017 ACCEPTED FOR PUBLICATION 29 November 2017 PUBLISHED 13 December 2017 https://doi.org/10.1088/2053-1591/aa9e13 Mater. Res. Express 4 (2017) 125024

Synthesis of copper sulfides with different morphologies in DMF and water: catalytic activity for methyl orange reduction

Sponge like Ni/NiO composites (pristine or doped with Cu or Co) were synthesized using a facile complex decomposition method and utilized as dye reduction catalysts in the presence of sodium borohydride as reductive agent. Ethylenediamine and metal nitrates along with ethanol are the only reagents used and calcination can be performed in air atmosphere at temperatures as low as 300 °C. Powder X-ray diffraction patterns revealed that the samples consist of a mixture of metallic and oxide phases in terms of both nickel and dopant (Cu or Co). Obtained pores are in micrometre scale and pore-formation mechanisms based on plausible routes were postulated. Field-emission scanning electron microscopy and energy dispersive spectra were used to investigate the microstructural features as well as the chemical compositions of the complex and calcined samples. Catalytic reduction of methylene blue with NaBH4 was chosen as an environmental reaction which can be monitored by time dependent UV–vis spectroscopy and the composite samples were put to test in order to investigate in terms of activity and robustness. The optimized sample was able to decolorize 97 percent of the dye after 370 s and retained its activity even after 5 consecutive reaction runs without re-generation protocols.

Alireza Rahmani

Papers

Cu(BDC) as a catalyst for rapid reduction of methyl orange: room temperature synthesis using recycled terephthalic acid

Efficient Synthesis of Some New Chromenopyrimidine Azo- Dyes Catalyzed by Cu/SBA-15

Novel Synthesis of Some 2-Aminochromene Derivatives using Nano-sized Zirconium Oxide as Catalyst

Synthesis of copper sulfides with different morphologies in DMF and water: catalytic activity for methyl orange reduction

Sponge like M-doped Ni/NiO (M = Cu, Co) composites and their catalytic activity toward dye reduction