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Expansive soils are generally characterised by their volume change when subjected to variation in water content. This may result in significant damage to supported and nearby structures. In this study, the swelling properties of bentonite material as an expansive soil are first determined. The expansive soil is then improved using two different approaches, namely, micro-metakaolin (Mm) and ferric chloride (FeCl3) solution. The optimum percentages for both additives are determined using laboratory experiments, which are 25 and 1% for the Mm and the ferric chloride solution, respectively. The free swell index of the bentonite after being treated with Mm and ferric chloride solution at the optimum percentages is found to decrease by about 54 and 62%, respectively. Meanwhile, the swelling pressure for the expansive soil decreased by 33 and 43% when mixed with the same optimum values of Mm and ferric chloride solution, respectively. On the basis of the results obtained in this study, the addition of ferric chloride solution achieved better results compared with Mm. This improvement technique may be used to enhance the properties of expansive soils that support different construction engineering projects. [ABSTRACT FROM AUTHOR]

Wastewater treatment by adsorption onto activated carbon is effective because it has a variety of benefits. In this work, activated carbon prepared from rice husk by chemical activation using zinc chloride was utilized to reduce chemical oxygen demand from wastewater. The as-prepared activated carbon was characterized by scanning electron microscope, Fourier transform infrared spectroscopy and nitrogen adsorption/desorption analysis. The optimum conditions for maximum removal were achieved by studying the impact of various factors such as solution pH, sorbent dose, shaking time and temperature in batch mode. The results displayed that the optimum sorption conditions were achieved at pH of 3.0, sorbent dose of 0.1 g L−1, shaking time of 100 min and at room temperature (25 °C). Based on the effect of temperature, the adsorption process is exothermic in nature. The results also implied that the isothermal data might be exceedingly elucidated by the Langmuir model. The maximum removal of chemical oxygen demand by the activated carbon was 45.9 mg g−1. The kinetic studies showed that the adsorption process follows a pseudo-first order model. The findings suggested that activated carbon from rice husk may be used as inexpensive substitutes for commercial activated carbon in the treatment of wastewater for the removal of chemical oxygen demand. [ABSTRACT FROM AUTHOR]

Four solid adsorbents namely nanohydroxyapatite (NP), cetyltrimethyl ammonium bromide modified nanohydroxyapatite (NPB), and nanohydroxyapatite/chitosan composite either in acidic (NPS1) or basic media (NPS2) were prepared based on egg shell as a biosource. Solid materials were characterized by N2 adsorption/desorption isotherms, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and point of zero charges. The thermal, textural, and chemical properties of nanohydroxyapatite/chitosan composite prepared in basic medium were found to be more enhanced than the other three solid adsorbents with surface area and pore radius of 152.5 m²/g and 5.11 nm, respectively. pHPZC for all the prepared solid samples ranged between 6.8 and 7.5. Adsorption of hexavalent chromium were studied under different application condition such as the effect of adsorbent dosage, time, pH, initial Cr(VI) concentration, and temperature. The maximum adsorption capacities of chromium onto NP, NPS1, NPS2, and NPB (119.047, 131.578, 134.048, and 85.397 mg/g, respectively) were observed at pH 6. Thermodynamic and kinetic parameters proved that adsorption of Cr(VI) onto all the investigated solid adsorbents follow pseudo-second-order kinetic model, spontaneous, and endothermic adsorption process. [ABSTRACT FROM AUTHOR]

Calcium alginate beads (A), graphene oxide (GO) and GO/alginate beads composites (GA1, GA2 and GA3) as solid adsorbents were prepared and characterized by thermogravimetric curves (TGA), nitrogen adsorption/desorption curves, point of zero charge (pHPZC), X-ray difffractometer (XRD), transmission electron microscope (TEM) and Fourier-transform infrared spectroscopy (FTIR). Adsorption of 2, 4-dichlorophenoxyacetic acid as one of the most toxic applied herbicide in the fields worldwide was studied considering the effect of different adsorption parameters. Results revealed that the optimum adsorbent dosage and initial pH value were found 2.0 g/L and pH 6, respectively. Freundlich and Langmuir adsorption models were applied and the maximum adsorption capacity was confirmed by GA3 (150.4 mg/g). Kinetic and thermodynamic studies proved that the adsorption follows the pseudo-second order kinetic models (PSO) and the exothermic spontaneous physisorption process. [ABSTRACT FROM AUTHOR]

In this study, zinc oxide nanoparticles (ZnO) and nanohydroxyapatite (NHAP) were prepared in the presence of date palm pits extract (DPPE) and eggshells, respectively. Another four nanocomposites were prepared from ZnO and NHAP in different ratios (ZP13, ZP14, ZP15, and ZP16). DPPE and all nanomaterials were characterized using GC-MS, zeta potentials, particle size distributions, XRD, TEM, EDX, FTIR, and pHPZC. The characterization techniques confirmed the good distribution of ZnO nanoparticles on the surface of NHAP in the prepared composites. Particles were found to be in the size range of 42.3–66.1 nm. The DPPE analysis confirmed the presence of various natural chemical compounds which act as capping agents for nanoparticles. All the prepared samples were applied in the adsorption and photocatalytic degradation of methylene blue under different conditions. ZP14 exhibited the maximum adsorption capacity (596.1 mg/g) at pH 8, with 1.8 g/L as the adsorbent dosage, after 24 h of shaking time, and the static adsorption kinetic process followed a PSO kinetic model. The photocatalytic activity of ZP14 reached 91% after 100 min of illumination at a lower MB concentration (20 mg/L), at pH 8, using 1.5 g/L as the photocatalyst dosage, at 25 °C. The photocatalytic degradation of MB obeyed the Langmuir–Hinshelwood first-order kinetic model, and the photocatalyst reusability exhibited a slight loss in activity (~4%) after five cycles of application. [ABSTRACT FROM AUTHOR]

In this study, electrospinning was used to fabricate xanthan gum (XF) and thiosemicarbazide/xanthan gum (TXF) nanofibers crosslinked with ferric ions for effective Pb 2+ adsorption. The produced nanofibers were investigated using several physicochemical methods. Both XF and TXF demonstrated thermal stability up to 800 °C, with mass losses of 79% and 75%, respectively. TXF had a surface area of 153.4 m 2 g -1 and point of zero charge at pH 6.7. ATR-FTIR analysis revealed the existence of surface chemical functional groups such as -NH 2 , -NH, and -C[double bond, length as m-dash]S owing to thiosemicarbazide reinforcement. XF and TXF displayed maximum adsorption capacities of 211.65 and 289.18 mg g -1 at pH 6, 2.0 g L -1 nanofiber dose, 22 °C, and after 40 min of contact shaking time. The adsorption process was investigated using several nonlinear adsorption models as well as by desorption and reusability investigations. Thermodynamics examination demonstrated the spontaneous, endothermic physisorption of Pb 2+ onto XF and TXF. Ethylenediaminetetraacetic acid was selected as the most efficient eluent for Pb 2+ removal from the nanofiber surfaces, with desorption efficiencies of 100% and 97% for XF and TXF, respectively. TXF and XF revealed remarkable sustainability, with reductions in adsorption capacities of only 7% and 12% of the initial removal efficiency after 10 cycles of adsorption/desorption, respectively. As a solid adsorbent for the removal of heavy metal cations, the produced TXF nanofiber demonstrated great sustainability and environmental friendliness., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this work., (This journal is © The Royal Society of Chemistry.)