Synthesis of iron oxide nanoparticles mediated by Camellia sinensis var. Assamica for Cr(VI) adsorption and detoxification.

Environment-benign synthesis of nanoparticles (NPs) are of great importance. Plant-based polyphenols (PPs) are electron donor analytes for the synthesis of metal and metal oxide NPs. This work produced and investigated iron oxide nanoparticles (IONPs) from PPs of tea leaves of Camellia sinensis var. assamica for Cr(VI) removal. The conditions for IONPs synthesis were using RSM CCD and found to be optimum at a time of 48 min, temperature of 26 °C, and iron precursors/leaves extract ratio (v/v) of 0.36. Further, these synthesized IONPs at a dosage of 0.75 g/L, temperature of 25 °C, and pH 2 achieved a maximum of 96% Cr(VI) removal from 40 mg/L of Cr(VI) concentration. The exothermic adsorption process followed the pseudo-second-order model, and Langmuir isotherm estimated a remarkable maximum adsorption capacity (Qm) of 1272 mg g-1 of IONPs. The proposed mechanistic for Cr(VI) removal and detoxification involved adsorption and its reduction to Cr(III), followed by Cr(III)/Fe(III) co-precipitation.

Combinatorial optimality of functional groups, process parameters, and Pd(II) adsorption-desorption characteristics for commercial anion exchange resins-synthetic electroless plating systems.

Considering combinatorial optimality of functional group analysis, speciation, solution chemistry complexity, Pd(II) adsorption-desorption characteristics, this article addresses the competence and efficacy of anion exchange resins namely Amberlite IRA958, Dowex Marathon MSA, Lewatit TP214, and Amberlyst A21 commercial resins. Based on preliminary batch adsorption experiments conducted in the range of 2-10 pH, 0.2-2 g L-1 adsorbent dosage, and 5-1080-min contact time, the optimal adsorption process parameters refer to 4 pH, 1.6, and 1.4 g L-1 adsorbent dosage, and 840- and 720-min contact time for Amberlite IRA958 and Dowex Marathon MSA resins, respectively. Among alternate models, the best-fit models refer to the Freundlich isotherm and pseudo-second-order kinetic models to represent Pd(II) adsorption data obtained for both Dowex Marathon MSA and Amberlite IRA958 resins. Based on the Langmuir isotherm, the maximum monolayer adsorption capacity was evaluated to be 185.16 and 166.67 mg g-1 for Dowex Marathon MSA and Amberlite IRA958 resins, respectively. For model electroless plating solutions as adsorbate system possessing desired solution chemistry complexity and resin cost, nitrogen- and oxygen-containing Amberlyst A21 resin is concluded to be optimal resin. This is not in agreement with the generalized rule of thumb that considers sulfur-nitrogen functional group containing commercial resins to be effective than resins with nitrogen-oxygen functional groups. Due to functional group interactions with the noble metal, no other by-products or exchanged chemicals have been produced in due course of Pd(II) adsorption process, which can be also regarded as an added advantage of the process. Graphical abstract.

Role of EDTA on the Pd(II) adsorption characteristics of chitosan cross-linked 3-amino-1,2,4-triazole-5-thiol derivative from synthetic electroless plating solutions.

This article targets the efficacy of chitosan cross-linked 3-Amino-1,2,4-triazole-5-thiol derivative for the recovery of Pd from synthetic electroless plating solutions (ELP) whose solution chemistry complexity is brought forward with ethylenediaminetetraacetic acid (EDTA), ammonium hydroxide (NH4OH), and surfactant (cetyl trimethyl ammonium bromide (CTAB)). Batch adsorption characteristics of the resin were investigated in the parametric range of 2-10 pH, 0.2-2 g L-1 adsorbent dosage, 5-1080 min contact time, 50-300 mg L-1 Pd concentration and 25-60 °C operating temperature. Equilibrium, kinetic and thermodynamic model fitness studies were also considered. Pd(II) adsorption characteristics were determined using NaOH, KOH and HCl solutions with variant eluent concentrations (0.1-2 N). The solution chemistry complexity has been evaluated to have profound impact in detrimentally influencing Pd sorption characteristics of the CH-AZ resin. The resin has been characterized to be highly effective for Pd removal from synthetic ELP solutions but with moderate efficacy towards the noble metal recovery and reuse.