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1. Melamine-based functionalized graphene oxide and zirconium phosphate for high performance removal of mercury and lead ions from water

   https://doi.org/10.1039/d0ra07546a  

   Bakry, Ayyob M. ; Awad, Fathi S. ; Bobb, Julian A. ; Ibrahim, Amr A. ; El-Shall, M. Samy ( October 2020 , RSC Advances)

   null (Ed.)

   Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg( ii ) and Pb( ii ) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen's functional groups attached to the partially reduced GO nanosheets to effectively capture Hg( ii ) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg( ii ) with a capacity of 651 mg g −1 and very fast kinetics resulting in a 100% removal of Hg( ii ) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen's functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb( ii ) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb( ii ) with a capacity of 681 mg g −1 and 1000 mg g −1 using an adsorbent dose of 1 g L −1 and 2 g L −1 , respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb( ii ) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L −1 . In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb( ii ), 99% for Hg( ii ), Cd( ii ) and Zn( ii ), 94% for Cu( ii ), and 90% for Ni( ii ) while at a higher concentration of 250 ppm the removal efficiency for Pb( ii ) is 95% compared to 23% for Hg( ii ) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg( ii ) and Pb( ii ), respectively from contaminated water. 

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2. Heteroatom decorated polythiourethane sorbent for copper ( II ) extraction in wastewater treatment

   https://doi.org/10.1002/pen.26752  

   Aurangzeb, Noshaba ; Zulfiqar, Sonia ; Khosa, Muhammad Kaleem ; Slovák, Václav ; Maamoun, Ahmed Abdelhamid ; Forrester, Michael ; Sarwar, Muhammad Ilyas ; Cochran, Eric W ( July 2024 , Polymer Engineering & Science)

   Copper ions in wastewater present substantial environmental hazards, toxic to aquatic species and prone to bioaccumulation. Addressing this, we present a novel cross‐linked polythiourethane (C‐PTU) as a promising chelating adsorbent for the effective removal of copper ions from wastewater. A new monomer, 5‐(2,2,2‐trifluoroacetamide) benzene‐1,3‐bis(carbonyl) isothiocyanate (TFA‐ITC), was synthesized and further condensed with a 1,4‐butane diol to produce a trifluoroacetamide functionalized polythiourethane (TFA‐PTU) and subsequently generating amine functionalized polythiourethane (A‐PTU). The cross‐linking reaction was carried out through amino groups present on the polymer backbone with terephthaloyl chloride, resulting in the formation of C‐PTU. The monomer and polymers underwent characterization using Fourier transform infrared,¹H, and¹³C nuclear magnetic resonance spectroscopy, with X‐ray diffraction analyzing the resin's chain alignment. Thermogravimetric and differential scanning calorimetry assessed C‐PTU's thermal properties. The adsorption process for Cu(II) ions was studied using atomic absorption spectroscopy, optimizing conditions for maximal uptake. Results revealed that C‐PTU exhibited a significant adsorption capacity for Cu(II) ions, reaching 67% after a 2 h contact time, with optimal adsorption occurring at pH 6. The Langmuir adsorption isotherm described the sorption mechanism, indicating favorable monolayer cation adsorption via coordination with donor sites on C‐PTU. This research presents a viable solution for copper ion contamination in wastewater, illustrating C‐PTU as an efficient, environmentally friendly adsorbent, marking progress toward cleaner water resources.

    

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3. Rice husk based nanocellulose scaffolds for highly efficient removal of heavy metal ions from contaminated water

   https://doi.org/10.1039/D0EW00545B  

   Zhan, Chengbo ; Sharma, Priyanka R. ; He, Hongrui ; Sharma, Sunil K. ; McCauley-Pearl, Alexis ; Wang, Ruifu ; Hsiao, Benjamin S. ( October 2020 , Environmental Science: Water Research & Technology)

   null (Ed.)

   Rice husks are an agricultural residue of great annual production and have a high cellulose content. In this study, we have prepared highly charged carboxyl cellulose nanofibers (CNFs) from rice husks using the TEMPO-oxidation method and the extracted CNFs were evaluated as an adsorbent for the removal of lead( ii ) and lanthanum( iii ) (Pb( ii ) and La( iii )) ions from contaminated water. Three different forms of nanocellulose adsorbents were prepared: suspension, freeze-dried, and nanocomposite containing magnetic nanoparticles, where their adsorption performance was tested against the removal of the two chosen heavy metal ions. The maximum adsorption capacity of rice husk based CNFs was found to be the highest in the nanocellulose suspension, i.e. , 193.2 mg g −1 for Pb( ii ) and 100.7 mg g −1 for La( iii ). The separation of the used adsorbent in the suspension was further facilitated by the gelation of the CNFs and metal cations, where the resulting floc could be removed by gravity-driven filtration. The absorption mechanism of the investigated CNF system is mainly due to electrostatic interactions between negatively charged carboxylate groups and multivalent metal ions. It was found that 90% lanthanum content in the form of lanthanum oxychloride (determined by X-ray powder diffraction) could be obtained by incinerating the CNF/LaCl 3 gel. This study demonstrates a viable and sustainable solution to upcycle agricultural residues into remediation nanomaterials for the removal and recovery of toxic heavy metal ions from contaminated water. 

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4. Remarkable Acid Stability of Polypyrrole‐MoS 4 : A Highly Selective and Efficient Scavenger of Heavy Metals Over a Wide pH Range

   https://doi.org/10.1002/adfm.201800502  

   Xie, Linxia ; Yu, Zihuan ; Islam, Saiful M. ; Shi, Keren ; Cheng, Yahan ; Yuan, Mengwei ; Zhao, Jing ; Sun, Genban ; Li, Huifeng ; Ma, Shulan ; et al ( March 2018 , Advanced Functional Materials)

   The new material polypyrrole/MoS₄²⁻(MoS₄‐Ppy), prepared by ion‐exchange of NO₃‐ of NO₃‐Ppy with MoS₄²⁻, displays high acid stability and excellent uptake for heavy metal ions such as Hg²⁺, Ag⁺, Cu²⁺, and Pb²⁺. The different maximum adsorption capacities (q_m) for Cu²⁺, Pb²⁺, Hg²⁺, and Ag⁺depend on the various binding modes arising from the different thiophilicity of these metal ions. The removals of Ag⁺and Pb²⁺reach >99.6% within 5 min, and for highly toxic Hg²⁺, >98% removal achieves at 1 min. At strong acid limit, the exceptionalq_m(Ag⁺) of 725 mg g⁻¹places the MoS₄‐Ppy at the top of materials for such removal. Uptake kinetics of Ag⁺, Hg²⁺, and Pb²⁺is extremely fast: >99.9% removal rates at wide pH range (0.5–6) within 1–5 min. Also, at strongly acidic conditions (pH ≈ 1), for highly toxic Hg²⁺, <2 ppb concentration can be achieved, accepted as safe limit. The MoS₄‐Ppy demonstrates an outstanding ability to separate low‐concentrated Ag⁺from high concentrated Cu²⁺especially under strong acidic conditions (pH ≈ 1), showing a large separation factor SF_Ag/Cu(K_d^Ag/K_d^Cu) of 10⁵(>100). MoS₄‐Ppy is a superior and novel sorbent material for water remediation applications as well as precious metals recovery.

    

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5. The role of cysteine and sulfide in the interplay between microbial Hg( ii ) uptake and sulfur metabolism

   https://doi.org/10.1039/c9mt00077a  

   Thomas, Sara A. ; Catty, Patrice ; Hazemann, Jean-Louis ; Michaud-Soret, Isabelle ; Gaillard, Jean-François ( May 2019 , Metallomics)

   Biogenic thiols, such as cysteine, have been used to control the speciation of Hg(ii) in bacterial exposure experiments. However, the extracellular biodegradation of excess cysteine leads to the formation of Hg(ii)–sulfide species, convoluting the interpretation of Hg(ii) uptake results. Herein, we test the hypothesis that Hg(ii)–sulfide species formation is a critical step during bacterial Hg(ii) uptake in the presence of excess cysteine. An Escherichia coli (E. coli) wild-type and mutant strain lacking the decR gene that regulates cysteine degradation to sulfide were exposed to 50 and 500 nM Hg with 0 to 2 mM cysteine. The decR mutant released ∼4 times less sulfide from cysteine degradation compared to the wild-type for all tested cysteine concentrations during a 3 hour exposure period. We show with thermodynamic calculations that the predicted concentration of Hg(ii)–cysteine species remaining in the exposure medium (as opposed to forming HgS(s)) is a good proxy for the measured concentration of dissolved Hg(ii) (i.e., not cell-bound). Likewise, the measured cell-bound Hg(ii) correlates with thermodynamic calculations for HgS(s) formation in the presence of cysteine. High resolution X-ray absorption near edge structure (HR-XANES) spectra confirm the existence of cell-associated HgS(s) at 500 nM total Hg and suggest the formation of Hg–S clusters at 50 nM total Hg. Our results indicate that a speciation change to Hg(ii)–sulfide controls Hg(ii) cell-association in the presence of excess cysteine.

    

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