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a b s t r a c tIn this study, an adsorbent based on nanosilica molecules was synthesized by chemical activation and changing the structure of a sodium silicate )Na 2 SiO 3 (. The adsorbent was characterized by scanning electron microscope/energy-dispersive X-ray spectroscope, X-ray diffraction analysis, transmission electron microscope, and Brunauer-Emmett-Teller analysis for morphologic properties and determination of specific surface area. Sorption experiments were carried out to evaluate the effects of variables, such as initial dye concentration, contact time, and pH on the dye removal. Different isotherm and kinetic models were used to evaluate the sorption equilibrium and describe the sorption process. More than 75% removal efficiency was obtained within 15 min at adsorbent dose of 10 g/L for initial dye concentration of 150 mg/L. The maximum sorption capacity was found to be 92.9 mg/g at pH 10 and 70.9 mg/g at pH 9 for RB and MB, respectively. The best fit was achieved by the Langmuir isotherm equation (R 2 values = 0.99 and 0.98) for RB and MB, respectively. The kinetic studies showed that the RB and MB dye sorption onto the nanoadsorbent was best described by the pseudo-second-order kinetic model. This study showed that the sodium silicate nanoadsorbent can be an ideal adsorbent for dye removal and may also be used in environmental research in other fields.

Purpose This study aims to activated carbon prepared from pistachio waste by using phosphoric acid as chemical activator agent. Activated carbon adsorbents were prepared from pistachio waste by using phosphoric acid as chemical activator agent. Design/methodology/approach The optimum conditions for the highest adsorption performance were determined by central composite design (CCD). The adsorbent was used for the adsorption of dye reactive black 5 (RB5), and the parameters affecting the adsorption were discussed like pH, initial concentration, contact time and adsorbent dosage. The adsorbent synthesized has been characterized by FTIR spectroscopy and scanning electron microscopy. The kinetic models including pseudo-first-order, pseudo-second-order and intraparticle diffusion with Langmuir and Freundlich isotherm models were applied to investigate the kinetic and isotherms parameters. Findings When the dye concentration is 10 mg/L, RB5 dye removal rates reach 87.5 per cent. Moreover, the adsorption process of RB5 follows the pseudo-second-order kinetics and the Freundlich adsorption isotherm. Practical implications This study provided a simple and effective way to prepare activated carbon adsorbents from pistachio wastes. This way was conductive to protect environmental from a huge amount of agricultural waste produced and subsequent application for removal of pollutants from aqueous solutions. Originality/value The activated carbon adsorbents are prepared via chemical activation, which is prepared with pistachio wastes. There are two main innovations: one is that the novel adsorbents are prepared successfully by waste and the other is that the optimized conditions are designed by CCD.

Purpose The purpose of this paper is to analyze zero valent iron nanoparticles (NZVIs) by a novel green method, taken from Thymus vulgaris (TV) plant extract, were synthesized and applied to degrade reactive black 5 (RB5) azo dye. Design/methodology/approach The optimum conditions for the highest removal of RB5 dye were determined. Characterization of NZVIs was done by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The NZVIs were used for the removal of dye RB5, and the parameters affecting were discussed like pH, initial concentration, contact time and NZVIs dosage. Findings The characterization results of NZVIs by SEM, TEM, FTIR and XRD show that polyphenols, organic acids and proteins reduce not only the green synthesis of NZVIs but also the aggregation of nanoparticles. The maximum dye removal efficiency of 99.6 per cent occurred at pH 4, NZVIs dose of 600 mg/L, and contact time of 5 min. The adsorption of RB5 dye onto the NZVIs surface and scavenging of the azo bond (−N = N) by the strong reduction of NZVIs were the proposed mechanisms for dye removal. The application of NZVIs to treat wastewater containing reactive dye shows high degradation efficiency. Research limitations/implications The findings may greatly benefit the application of the NZVIs taken from Thymus vulgaris (TV) in the fields of dye adsorption. Practical implications The present study is novel because it incorporated the morphological and structural properties of the synthesized NZVIs using a native plant of Iran and studied the capability of green-synthesized NZVIs to remove RB5 as a water contaminant. Social implications The native plant presented here can be developed for reduced environmental pollution before discharge to accepted water. Originality/value The NZVIs is prepared via green-synthesized method, which is prepared with leaves of TV. There are two main innovations. One is that the novel NZVIs is prepared successfully by native plant via green-synthesized method. The other is that the optimized conditions were obtained for the removal of RB5 dye as a water contaminant. Furthermore, to the best of our knowledge, no study has ever investigated the removal of RB5 by NZVIs produced using a native plant in Iran.

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