Effective removal of Hg(II) ion from aqueous solutions by thiol functionalized cobalt ferrite magnetic mesoporous silica composite

Clay-polymer nanocomposites for effective water treatment: opportunities, challenges, and future prospects

The metal intoxication and its associated adverse effects to humans have led to the research for development of water treatment technologies from pollution hazards. Therefore, development of cheaper water remediation technologies is more urgent than ever. Clays and clay minerals are naturally occurring, inexpensive, non-toxic materials possessing interesting chemical and physical properties. As a result of interesting surface properties, these have been developed as efficient absorbent in water remediation. Recently, clay-polymer nanocomposites have provided a cost-effective technological platform for removing contaminants from water. Covering research advancements from past 25 years, this review highlights the developments in clay-polymer nanocomposites and their advanced technical applications are evaluated with respect to the background and issues in remediation of toxic metals and organic compounds from water. The extensive analysis of literature survey of more than two decades suggests that future work need to highlight on advancement of green and cost-effective technologies. The development of understanding of the interaction and exchange between toxin and clay-polymer composites would provide new assembly methods of nanocomposites with functional molecules or nanomaterials need to be extended to increase the detection and extraction limit to parts per trillion.

Highly reusable bentonite clay@biochar@Fe3O4 nanocomposite for Hg(II) removal from synthetic and real wastewater

The present research investigates the performance of bentonite clay@biochar@Fe₃O₄ nanocomposite in removing mercury ions (Hg²⁺) from aqueous media. The physical and structural properties of bentonite clay@biochar@Fe₃O₄ were determined using Brunauer-Emmett-Teller (BET), vibrating-sample magnetometer (VSM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), and Raman analyses. The highest uptake efficiency of Hg²⁺ was obtained at pH 6, Hg²⁺ concentration of 10 mg/L, contact time of 80 min, and the composite dose of 1.5 g/L. Under these conditions, the uptake efficiency of bentonite clay@biochar@Fe₃O₄ and bentonite clay was obtained as 98.78% and 97.67%, respectively, which are remarkable values. Also, the q_max values in Hg²⁺ removal using bentonite clay@biochar@Fe₃O₄ and bentonite clay were obtained as 66.66 and 60.98 mg/g, respectively. Moreover, the uptake process of Hg²⁺ ions using bentonite clay@biochar@Fe₃O₄ nanocomposite and bentonite was spontaneous, physical, favorable, and exothermic. Besides, the impact of various divalent ions such as Co²⁺, Cu²⁺, Pb²⁺, Ni²⁺, and Zn²⁺ on the removal efficiency of Hg²⁺ was studied. The results showed that Co²⁺ and Zn²⁺ ions have the highest and lowest interference effect in Hg²⁺ removal, respectively. Also, the reusability of both adsorbents showed that they have high stability and can be used for at least 5 cycles with high uptake efficiency. Additionally, the removal efficiency of chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), Hg²⁺, As³⁺, and As⁵⁺ from real wastewater using bentonite clay@biochar@Fe₃O₄ was obtained as 37.5%, 28.9%, 65%, 60.5%, and 50%, respectively, indicating its remarkable performance.

S,N-rich luminous covalent organic frameworks for Hg2+ detection and removal

The challenge for simultaneous detection and removal of Hg²⁺ is the design of bifunctional materials bearing abundant accessible chelating sites with high affinity. Covalent-organic frameworks (COFs) are attracting more and more attention as potential bifunctional materials for Hg²⁺ detection due to their large specific surface area, ordered pores, and abundant chelating sites. Here, a new luminous S,N-rich COF_BTT-AMPD based on hydrophilic block unit of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AMPD) was constructed, which improved the solubility and affinity for Hg²⁺ greatly. Another S-rich fused-ring unit of benzotrithiophene tricarbalaldehyde (BTT) enhanced the conjugation of COF_BTT-AMPD, and the methyl-rich chains block unit of AMPD effectively suppressed the aggregation-caused quenching. Thus, the COF_BTT-AMPD emitted strong fluorescence at 546 nm in liquid and solid as well as different solvent with a wide pH range, which was used for the visual detection and removal of Hg²⁺ (detection limit: 2.6 nM, linear range: 8.6 × 10^-3-20 μM, monolayer adsorption capacity: 476.19 mg g^-1) successfully. COF_BTT-AMPD-based fabric and light-emitting diode coatings were further constructed to realize the visual detection of Hg²⁺ vapor. The results reveal the potential of S,N-rich luminous COF_BTT-AMPD for Hg²⁺ detection and remediation in the environment.

Mechanism of simultaneous lead and chromium removal from contaminated wastewater by a schwertmannite-like mineral

In this study, a schwertmannite-like mineral was synthesized for the removal of lead (Pb) and chromium (Cr) from contaminated wastewater. A shaking flask test was performed (150 r/min, 1 h) with FeSO₄·7H₂O, H₂O₂, Na₂SiO₃, and CaCl₂ added for the mineral synthesis reaction. Results show that optimal performance was achieved with the addition of 1.24 g/L FeSO₄·7H₂O, 0.75 g/L H₂O₂, 1.27 g/L Na₂SiO₃, and 0.44 g/L CaCl₂ at a water temperature of 28 °C, with coexisting ion (Na⁺, K⁺, Mg²⁺) concentrations of 1.50 mmol/L and 0.50 mmol/L EDTA as a complexing agent. Under these optimal conditions, maximum Pb and Cr removal rates of 95.08% and 97.99%, respectively, were achieved within the first 1 min of the mineral synthesis reaction, with the synthesis reaction completed by 6 min. The simultaneous removal of Pb and Cr during the schwertmannite-like material synthesis process occurred via electrostatic adsorption and coprecipitation. When the concentration of the complexing agent was increased from 0.75 to 6.03 mmol/L, the Pb removal rate decreased from 71.88 to 35.45%, and the Cr removal rate decreased from 95.13 to 75.07%, showing that Pb and Cr removal exhibited significant levels of inhibition. In contrast, varying reaction temperatures induced no significant differences. The Pb and Cr dissolution rates from Pb/Cr-containing schwertmannite-like minerals were 8.18% and 2.86% after 40 days, respectively. Therefore, the risk of secondary dissolution of heavy metals is small.

Adenosine-functionalized UiO-66-NH2 to efficiently remove Pb(II) and Cr(VI) from aqueous solution: Thermodynamics, kinetics and isothermal adsorption

A new zirconium-based adsorption material (UiO-66-AMP) was prepared by modifying UiO-66-NH₂ with 5-adenosine to effectively remove Pb(II) and Cr(VI) from wastewater. The SEM, EDS, XRS and FT-IR characterization confirmed the successful synthesis of UiO-66-AMP. We conducted a sets of experiments to test the adsorption effectiveness of UiO-66-AMP for Pb(II) and Cr(VI). The maximum adsorption capacity of UiO-66-AMP for Cr(VI) (pH=2) and Pb(II) (pH=4) are 196.60 and 189.69 mg/g, respectively. The adsorption process conforms to the pseudo-second-order and Langmuir models, which indicates that the adsorption is a single-layer chemical process. Gibbs free energy (∆G) indicates that the adsorption of Pb(II) is an exothermic reaction, while the adsorption of Cr(VI) is an endothermic reaction. At the same time, the adsorbent maintains excellent adsorption capacity at least after 4 cycles. The good adsorption performance of UiO-66-AMP towards the metal ions was attributed to the surface complexation and electrostatic interactions. Therefore, the new adsorbent has obvious application prospect to remove Pb(II) and Cr(VI) from wastewater.

Adsorption of lead ions from wastewater using nano silica spheres synthesized on calcium carbonate templates

Lead is a heavy metal that is bio accumulative and non-biodegradable that poses a threat to our health when it exists in excess in our bloodstream. It has found its way into wastewater from mostly chemical industrial processes. In this article, we investigated the adsorption and hence removal of lead (II) ions from wastewater in order to purify it for re-use in industrial processes or for plant and animal use. We synthesized nano silica hollow spheres (NSHS) and used them as adsorbents to remove lead ions from wastewater. When we characterized the NSHS using X-Ray diffraction, the amorphous nature of silica was evident with average crystal size of 39.5 nm. Scanning electron microscopy was used to determine the morphology of the adsorbent and the particles were found to be spherical in shape within a size range of 100–200 nm. Thermogravimetric analysis was used to determine the mass loss of NSHS which was ~2% at 800 °C. Our experimental results from adsorption studies showed that there was a linear relationship between temperature (27–60 °C) and adsorption efficiency and an inverse relationship between initial metal concentration (50–300 mg/L) and adsorption efficiency. At a maximum temperature of 60 °C and maximum initial metal concentration of 300 mg/L, the adsorption capacity was 200 mg/g and 262 mg/g, respectively while the adsorption efficiency was 99.6% and 87.4%, respectively. Our equilibrium and thermodynamic results revealed that the process was better modelled by the Langmuir adsorption isotherm (q_max = 266.89 mg/g and b = 0.89 L/mg). The adsorption process was both endothermic (ΔH = 97 kJ/mol) and spontaneous (ΔG = -22 kJ/mol). We can conclude that we were able to successfully synthesize NSHS, use them to remove lead (II) ions and the produced NSHS have a capacity that is higher than most other adsorbents investigated by other researchers.