The purpose of this study was to investigate the feasibility of activated carbons prepared from Macadamia nutshells as an efficient adsorbent for the removal of hexavalent chromium (Cr(VI)) from aqueous solutions. The activated carbon was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), CHNS analyzer and Brunauer-Emmett-Teller (BET). For effective removal of Cr(VI), the optimum parameters found were pH 2, 120 min of contact time and 0.2 g of sorbent. The adsorption data fitted well into the Freundlich model, suggesting a multilayer sorption process. The results demonstrated that Macadamia activated carbon could be used as cost-effective biosorbent for the treatment of aqueous solutions contaminated by Cr(VI) with an adsorption capacity of 22.3 mg g. The mode of removal involved adsorption and reduction of Cr(VI) to Cr(III).

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The synthesis of non-noble metal nanocrystals as cheaper alternatives to Pt for use as hydrogen evolution reaction (HER) electrocatalysts is highly desired for the future of renewable energy. In this...

Herein we report on the use of different metal precursors in the synthesis of MoSe2 nanomaterials in order to control their morphology. The use of Mo(CO)6 as the metal precursor resulted in the formation of wrinkled few-layer nanosheets, while the use of H2MoO4 as the metal precursor resulted in the formation of nanoflowers. To investigate the effect of the morphologies on their performance as catalysts in the hydrogen evolution reaction, electrochemical characterization was done using linear sweep voltammetry (LSV), cyclic voltammetry (CV), and electrical impedance spectroscopy (EIS). The MoSe2 nanoflowers were found to have superior electrochemical performance towards the hydrogen evolution reaction with a lower Tafel slope, on-set potential, and overpotential at 10 mA/cm2 compared to the wrinkled few-layer nanosheets. This was found to be due to the higher effective electrochemical surface area of the nanoflowers compared to the nanosheets which suggests a higher number of exposed edge sites in the nanoflowers.

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A wide variety of biomass materials have been used for the removal of toxic chromium(VI) by biosorption. The current study investigated the efficacy of Macadamia nutshells treated with sodium hydroxide, nitric acid, and the Fenton‐like reagent in the removal of Cr(VI). The adsorbents were characterized by FTIR, SEM, TGA, and elemental analysis. Effects of functional parameters influencing the adsorption of Cr(VI), solution pH (pH 1–11), contact time (5–250 min), concentration of adsorbent (1–10 g/L), and adsorbate concentration (10–200 mg/L) were investigated. The optimum conditions for biosorption were pH 1.4, adsorbent dose of 5 g/L, and 160 min of contact time. In all cases, the base‐treated adsorbent displayed superior performance compared to others, with highest percent removal of 98%. The adsorbate–adsorbent interactions were better explained by the Freundlich isotherm and the pseudo‐first‐order rate model. The Macadamia‐based adsorbents are potentially useful for Cr(VI) removal from aqueous solutions. Practitioner points Three different chemical activators were investigated for the modification of Macadamia surface. The base‐treated material exhibited the highest specific surface area of 12.1 m2/g. The Cr(VI) adsorption performance for the base‐treated material dwarfed the other materials. Excellent Cr(VI) removal efficiency in the presence of competitors was achieved.

Transition metal phosphides (TMPs) have emerged as efficient non-noble electrocatalysts for hydrogen evolution reaction (HER). However, the effect of their crystal phase on the electrocatalytic activity is rarely reported due...

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