Single evaluation and selection of functional groups containing N or O atoms to heavy metal adsorption: Law of electric neutrality

Polyethylenimine-grafted nitrogen-doping magnetic biochar for efficient Cr(VI) decontamination: Insights into synthesis and adsorption mechanisms

Herein, polyethylenimine (PEI)-grafted nitrogen (N)-doping magnetic biochar (PEI_MW@MNBC_BM) was synthesized, and characterization results showed that the microwave-assisted PEI grafting and ball milling-assisted N doping introduced abundant amino, pyridine N and pyrrole N structures onto biochar, which possessed high affinity to Cr(VI) in the anion form. The as-prepared PEI_MW@MNBC_BM displayed pH-dependence adsorption performance and high tolerance to co-existing ions with maximum uptake capacity of Cr(VI) identified as 183.02 mg/g. Furthermore, PEI_MW@MNBC_BM could bind Cr(VI) through electrostatic attraction, complexion, precipitation, reduction and pore filling. Especially, effective reduction of Cr(VI) was ascribed to cooperative electron transfer of partial oxygen-containing functional groups, intramolecular pyridine/pyrrole N, protonated amino and Fe²⁺ on the adsorbent, while oxygen-containing and amino functional groups from N-doping biochar and PEI synergistically complexed Cr(III) via providing lone pair electrons to form coordinate bonds. Furthermore, the stable precipitation was formed between Fe³⁺ and Cr(III). Additionally, the Cr(VI) elimination efficiency could maintain 95.83% even after four adsorption-desorption cycles, suggesting PEI_MW@MNBC_BM as a high-performance adsorbent for Cr(VI) contaminated water remediation.

Potential of sugarcane bagasse in remediation of heavy metals: A review

Presence of heavy metal (HM) ions in wastewater have emerged as among the most prominent issues for improving water quality and reducing it's consequences for the environment, animal and public health. This paper mainly focuses on the remediation of HM ions from wastewater utilizing the relatively inexpensive and widely accessible agricultural waste-Sugarcane Bagasse (SCB). For this, a brief understanding of HMs was discussed (by understanding the sources and toxicity of HM, advantages and shortcomings of conventional processes). Apart from that, to understand the potential of SCB, this review would provide vital information on employing SCB biosorbent in natural and modified forms for HM removal. Therefore, various ways of SCB modifications (including physical, chemical, and composite formation), essential optimal operational conditions (solution pH, dosage of biosorbent, initial metal concentration, contact time, agitation speed, temperature, suitable isotherm and kinetic model) and involving adsorption mechanism were also studied. Finally, significant study gaps were identified to facilitate future research since SCB has been confirmed as a potential bio-adsorbent for removing HM ions.

Versatile strategy of sulfanilamide antibiotics removal via microalgal biochar: Role of oxygen-enriched functional groups

Biochar (BC) adsorption has been widely acknowledged as an efficient approach for the removal of antibiotics. Despite the importance of oxygen-containing functional groups for the antibiotics removal, most of these may be obtained in BC only relying on the addition of oxidants. Herein, an environmentally friendly and oxygen-enriched functional groups adsorbent, namely Chlamydomonas BC (CBC), was fabricated via simple pyrolysis process. Then, the H-bonding, electron donor-acceptor and electrostatic attraction were identified as the main mechanisms regarding sulfathiazole (STZ) adsorption (506.38 mg/g). The carbon-oxygen functional groups on the surface of CBC (61%), especially -COOH and -OH, acted as a pivotal component. Additionally, further theoretical calculation led to the observation that STZ exhibited the highest chemical reactivity (η = 0.04), strong electron exchange capacity (μ = -0.16), remarkable electron accepting capacity (ω = 0.28) and excellent electron transfer efficiency (E_HOMO-E_LUMO gap = 0.29) under the influence of thiazolyl. The electrophilic sulfonamide group and the nucleophilic thiazole were identified as the main active sites of STZ. In summary, the results of this research provide a guiding role for the preparation of adsorbents driven by the structural characteristics of pollutants.

Removing miscellaneous heavy metals by all-in-one ion exchange-nanofiltration membrane

The composition of wastewater containing heavy metal mixtures is often complex and poses a serious threat to human and environmental health. Effective removal of a variety of heavy metal ions with a single technology is challenging, and the conventional split integrated technologies require multi-step processing and a massive footprint. For the first time, we achieve hierarchically integrating ion exchange and nanofiltration into all-in-one "iNF" membranes. The iNF membrane has a hierarchical structure with an interfacial polymerization layer and an ion exchange layer, which can achieve highly efficient indiscriminate heavy metal ion removal, overcoming the defect that traditional nanofiltration membranes can only remove single metal cations or oxyanions. The ion exchange layer can remove heavy metal ions through sulfonic acid groups and quaternary amine groups. In addition, the ion exchange layer can be regenerated by electro-deionization, which is meaningful for sustainable membrane usage. This facile, scalable, and compact integrated process shows outstanding potential and universal applicability in complex wastewater treatment.