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The structure and properties of basic metal-organic frameworks (MOFs) continue to exhibit low Cd(II) uptake and selectivity. Assembly of same zinc-based MOF building blocks into a dual-zinc MOF@MOF composite could offer a promising avenue for efficiently capturing Cd(II) from aqueous solutions. This paper reports a dual-zinc MOF@MOF (Zn-BTC@ZIF-8, DZM) adsorbent, which was constructed for boosting the performances of adsorption and separation. The adsorption behavior of Cd(II) onto DZM from aqueous solution is thoroughly examined at room temperature. Results indicates that the DZM demonstrates significant capability in capturing Cd(II), attributed to the synergistic effects of Zn-BTC and ZIF-8 with diverse active sites, appropriate pore sizes and shapes, stable dual zinc bonding interaction, and more. The maximum Cd(II) uptake capacity reached 150 mg/g, with rapid attainment of adsorption equilibrium within just 20 min, surpassing the performance of other reported adsorbents in the literature. The adsorption data align well with both the Freundlich and pseudo-second-order kinetic models. The process of adsorption is a process of spontaneous heat absorption and increasing degrees of freedom. Particularly noteworthy is the sustained effectiveness of DZM in capturing Cd(II) even after the fifth cycle. This research introduces a fresh approach to crafting desirable MOF@MOF configurations, thereby advancing their potential utility in Cd(II) removal from water. [Display omitted] • A new-style dual-zinc MOF@MOF (Zn-BTC@ZIF-8) adsorbent was first constructed. • The Zn-BTC@ZIF-8 composite exhibits adsorption performance toward Cd(II). • Double MOF structure is beneficial to expose more active sites and facilitate Cd(II) capture. [ABSTRACT FROM AUTHOR]

The objective of this study was to demonstrate the potential utilization of fly ash (FA), wood ash (WA), and metakaolin (MK) in developing new alkali-activated materials (AAMs) for the removal of cadmium ions from waste water. The synthesis of AAMs involved the dissolution of solid precursors, FA, WA, and MK, by a liquid activator (Na2SiO3 and NaOH). In concentrated solutions of the activator, the formation of an aluminosilicate gel structure occurred. DRIFT spectroscopy of the AAMs indicated main vibration bands between 1036 cm−1 and 996 cm−1, corresponding to Si-O-Si/Si-O-Al bands. Shifting vibration bands were seen at 1028 cm−1 to 1021 cm−1, indicating that the Si-O-Si/Si-O-Al bond is elongating, and the bond angle is decreasing. Based on the X-ray diffraction results, alkali-activated samples consist of an amorphous phase and residual mineral phases. The characteristic "hump" of an amorphous phase in the range from 20 to 40° 2θ was observed in FA and in all AWAFA samples. By the XRD patterns of the AAMs obtained by the activation of a solid three-component system, a new crystalline phase, gehlenite, was identified. The efficiency of AAMs in removing cadmium ions from aqueous solutions was tested under various conditions. The highest values of adsorption capacity, 64.76 mg/g (AWAFA6), 67.02 mg/g (AWAFAMK6), and 72.84 mg/g mg/g (AWAMK6), were obtained for materials activated with a 6 M NaOH solution in the alkali activator. The Langmuir adsorption isotherm and pseudo-second kinetic order provided the best fit for all investigated AAMs. [ABSTRACT FROM AUTHOR]

This study aimed to assess the sorption capacity of a natural sorbent, specifically birch bark (BB), and its modification using chemical reagents, including nitric and hydrochloric acid, sodium hydroxide, and chloride. The objective of the chemical modification was to enhance the sorption capacity of the heavy metals cadmium(II), chromium(VI), and manganese(II). The most effective modification for adsorbing cadmium and manganese from aqueous solutions was achieved by treating the sorbent with a 0.1 M sodium hydroxide solution (BBNa). Conversely, in the case of chromium, each modification adversely affected its adsorption by the sorbent. Concentrations of the solutions were analyzed using atomic absorption spectrometry at appropriate time intervals. The adsorption process was described using Langmuir, Freundlich, and Temkin isotherms. The Freundlich isotherm provided the best fit for cadmium and chromium (R2 = 0.988 and 0.986, respectively), while the Langmuir isotherm was most suitable for manganese (R2 = 0.996). The sorption capacity varied for each metal ion: Cd (II)—33.13 mg/g, Cr (VI)—35.98 mg/g, and Mn (II)—24 mg/g for the highest concentration tested. This study employed pseudo–first-rate order, pseudo–second-rate order model kinetics, and the Weber–Morris model to examine the adsorption kinetics. The pseudo–second-rate order kinetics demonstrated the best fit (R2 > 0.94) for each heavy metal, which underlines the process's chemical nature. [ABSTRACT FROM AUTHOR]

It is vital to remove cadmium from wastewater because of its potential harm to the natural environment and human health. It was found that sulfate-reducing bacteria (SRB) had a good fixing effect on Cd under a strict anaerobic environment. However, there are few reports on the immobilization effect and mechanism of SRB on Cd in an anoxic environment. This study revealed the effects of initial Cd2+ concentration, initial SO42− concentration, temperature, pH, and C/N ratio on the immobilization of Cd2+ by SRB in aqueous solution under an anoxic environment. The experimental results showed that under the conditions of initial concentration of Cd2+ within 0 mg/L~30 mg/L, initial concentration of SO42− within 1200 mg/L, temperature within 25 °C~35 °C, pH neutral, and C/N ratio of 20:1, the immobilization rate of Cd2+ by SRB is above 90%. The characterization results showed that bioadsorption and chemical precipitation were the main mechanisms of SRB immobilization of Cd2+ in an anoxic environment. [ABSTRACT FROM AUTHOR]

Cadmium (Cd2+) pollution in soil and water bodies is a significant environmental concern, necessitating effective remediation strategies. Traditional methods often fall short in efficiency, cost-effectiveness, and environmental sustainability. This study develops and evaluates the effectiveness of chitosan–gelatin–hydroxypropyl methylcellulose (CS-GEL-HPMC) membranes for Cd2+ removal from polluted environments. CS-GEL-HPMC membranes were synthesized with varying HPMC concentrations. Their structural and morphological characteristics were analyzed using UV–visible absorption spectroscopy and FT-IR. The membranes' stability across different pH levels and their morphological traits were assessed. The adsorption efficiency for Cd2+ ions was evaluated in both aqueous solutions and soil environments under varying conditions of pH, initial ion concentration, and contact time. The CS-GEL-HPMC membranes demonstrated significant structural integrity and stability, especially at higher HPMC concentrations. UV–visible and FT-IR analyses confirmed the successful integration of HPMC into the CS-GEL matrix. In aqueous solutions, the membranes exhibited efficient Cd2+ adsorption, with the best performance observed for the CS30-GEL30-HPMC40 membrane. The adsorption capacity was influenced by contact time, initial Cd2+ concentration, and pH. In soil treatments, the membranes effectively reduced Cd2+ concentrations, with higher membrane dosages yielding better results. The incorporation of additives like (hydroxyapatite) HAP, fly ash (FA), and cement further enhanced the remediation efficiency. In summary, CS-GEL-HPMC membranes, particularly when combined with additives, emerge as a promising, sustainable solution for Cd2+ remediation in both soil and water bodies. This study highlights the potential of biopolymer-based composites in environmental clean-up efforts, offering a novel approach that is both effective and eco-friendly. [ABSTRACT FROM AUTHOR]

Cadmium is a toxic metal that can contaminate water sources and pose serious health risks to humans and the environment. Therefore, there is a need for developing low-cost and eco-friendly methods for cadmium removal from water. In this research, we investigated the efficacy of barley straw in removing cadmium ions from aqueous solutions. The adsorbent utilized was laboratory-scaled barley straw that underwent pulverization via standard ASTM sieves, specifically those within the 40 to 120-mesh sieve size range. The functionalization of barley straw was achieved via treatment with a 0.8 M NaOH solution. The adsorbent was subsequently characterized by FTIR analysis to identify the presence of functional groups. The FTIR analysis indicated that the modification of barley straw led to an elevation in the stretch vibration band of hydroxyl and carboxyl groups. At the optimized experimental condition, a cadmium removal efficiency of up to 98.60% was achieved. These results demonstrate the potential of barley straw as an effective adsorbent for removing cadmium ions from aqueous solutions. [ABSTRACT FROM AUTHOR]