In this study, a novel biosorbent is prepared from the pods of Bauhinia variegata is used for defluoridation of the fluoride contaminated water. It is an eco-friendly and economically feasible material. Comparison of adsorption capacity of Physically Treated Bauhinia (PTB) and Chemically Treated Bauhinia (CTB) are carried in this work. Characterization studies like SEM, EDS, FTIR, and XRD are executed to analyze surface morphology and functional groups in PTB and CTB. The experimental procedure was implemented in a batch process where the operating constraints such as dosage, pH, initial fluoride concentration, time, and temperature are varied to attain optimized efficiency. PTB and CTB yield an adsorption capacities of 10.90 mg/g and 15.45 mg/g respectively in the batch process. PTB adheres fluoride in monolayer formation whereas CTB forms multilayer adsorption. The adsorption process was described by the Pseudo first-order model to state the mechanism of physisorption. The negative values of thermodynamic parameters indicate spontaneity and favorable conditions for adsorption process. As CTB has a higher adsorption capacity than PTB, the batch study has been extended to column adsorption. Bed depth, initial fluoride concentration, and flow rate are the experimental variables used to acquire breakthrough curves. Simplified column models like Adam-Bohart, Thomas, and Yoon-Nelson models were analyzed. In column studies, Yoon-Nelson model fitted well in describing the process of adsorption. The maximum adsorption capacity acquired during the column process was found to be 1.176 mg/g with a bed depth of 5 cm and a flow rate of 5 ml/min. Thus, the innocuous and sustainable adsorbent is developed and serves as an excellent defluoridation agent.

It is highly desirable but remains extremely challenging to develop a facile strategy to prepare adsorbent for dealing with heavy metal pollution in water. Here, we report a facile approach for preparing sulfydryl-functionalized graphene oxide (S-GO) by cross-linking method with an unprecedented adsorption capacity and ultrahigh selectivity for efficient Hg(II) removal. The adsorbents exhibit a prominent performance in capturing Hg(II) from wastewater with a record-high adsorption capacity of 3490 mg/g and rapid kinetics to reduce Hg(II) contaminants below the discharge standard of drinking water (2 ppb) within 60 min under a wide pH range even in the coexistent of other interfering metal ions. In addition, the adsorbents can be also easily recycled and reused multiple times with no apparent decline in removal efficiency. Considering the broad diversity, we developed also a magnetic Fe₃O₄/S-GO adsorbent by a simple chemical cross-linking reaction to achieve rapid separation of S-GO from their aqueous solution. In addition, the adsorbents were successfully applied in dealing with the practical industrial wastewater. The results indicate the potential of rationally designed sulfydryl-functionalized graphene oxide for high performance Hg(II) removal.

One of the strategies to realize a nitrogen cycle society, we attempted to recover ammonium ions from industrial wastewater, especially sewage water with adsorbent materials. We have developed an adsorbent with high ammonium selectivity based on copper hexacyanoferrate and granulated it as pellets. Using a compact column system filled with this granule adsorbent, ammonium ions were recovered from sewage containing 1000–1500 mg-NH₄⁺/L ammonium ions. Despite the coexistence of many metal ions, the adsorbent selectively and stably adsorbed ammonium ions. Furthermore, it was shown that the saturated adsorbent can be regenerated by flowing a potassium ion solution through a column adsorbent to desorb ammonium ions. In other words, the column can be used repeatedly, and there was almost little deterioration in adsorption even after 250 cycles. In addition, it was shown that by increasing the number of stages of this column, it is possible to sufficiently reduce the ammonium in the adsorbent solution and recover the concentrated ammonium solution.

Hydrochar (HC) serves as a promising adsorbent to remove the cadmium from aqueous solution due to porous structure. The chemical aging method is an efficient and easy-operated approach to improve the adsorption capacity of HC. In this study, four chemical aging hydrochars (CAHCs) were obtained by using nitric acid (HNO₃) with mass fractions of 5% (N5-HC), 10% (N10-HC), and 15% (N15-HC) to age the pristine HC (N0-HC) and remove the Cd²⁺ from the aqueous solution. The results displayed that the N15-HC adsorption capacity was 19.99 mg g⁻¹ (initial Cd²⁺ concentration was 50 mg L⁻¹), which increased by 7.4 folds compared to N0-HC. After chemical aging, the specific surface area and oxygen-containing functional groups of CAHCs were increased, which contributed to combination with Cd²⁺ by physical adsorption and surface complexation. Moreover, ion exchange also occurred during the adsorption process of Cd²⁺. These findings have important implications for wastewater treatment to transform the forestry waste into a valuable adsorbent for Cd²⁺ removal from water.

Biomass of Java plum (JP) and amaltash (AT) seeds were employed to remove arsenic from synthetic wastewater, cost effectively. The prepared biomasses were characterized by FE-SEM, EDX, FTIR, XRD, and ICP techniques. Experimentation the optimization study has been carried out by using Design-software 6.0.8. Response surface methodology has been applied to design the experiments where we have used three factors and three levels Box-Behnken design (BBD). Arsenic removal ability of bio-sorbents was evaluated and optimized by varying pH, adsorbent dose concentration of arsenic in synthetic wastewater. For 2.5 mg/L arsenic concentration and 80 mg adsorbent dose at pH 8.8 Java plum seeds (JP) based bio-adsorbent removed ∼93% and amaltash seeds (AT) based bio-adsorbent removed ∼91% arsenic from synthetic wastewater. The adsorption behaviour better explained following Freundlich model (R² = 0.99) compared to Temkin model (R² = 0.986) for As (III) ions. The adsorption capacity was 1.45 mg g⁻¹ and 1.42 mg g⁻¹ for JP and AT, respectively after 80 min under optimal set of condition. The adsorption kinetics was explained by either pseudo-first order model or Elovich model.

Polyethylene terephthalate (PET) is a possible key component of nanoplastics in water environments, which can migrate pollutants through co-transport. In this regard, the co-transport of endocrine disruptors (such as bisphenol A, BPA) by nanoplastics is of emergent concern because of its cytotoxicity/bioaccumulation effects in aquatic organisms. In this work, a computational study is performed to reveal the BPA adsorption mechanism onto PET nanoplastics (nanoPET). It is found that the outer surface of nanoPET has a nucleophilic nature, allowing to increase the mass transfer and intraparticle diffusion into the nanoplastic to form stable complexes by inner and outer surface adsorption. The maximum adsorption energy is similar (even higher) in magnitude with respect to nanostructured adsorbents such as graphene, carbon nanotubes, activated carbon, and inorganic surfaces, indicating the worrying adsorption properties of nanoPET. The adsorption mechanism is driven by the interplay of dispersion (38–49%) and electrostatics effects (43–50%); specifically, dispersion effects dominate the inner surface adsorption, while electrostatics energies dominate the outer surface adsorption. It is also determined that π–π stacking is not a reliable interaction mechanism for aromatics on nanoPET. The formed complexes are also highly soluble, and water molecules behave as non-competitive factors, establishing the high risk of nanoPET to adsorb and migrate pollutants in water ecosystems. Furthermore, the adsorption performance is decreased (but not inhibited) at high ionic strength in salt-containing waters. Finally, these results give relevant information for environmental risk assessment, such as quantitative data and interaction mechanisms for non-biodegradable nanoplastics that establish strong interactions with pollutants in water.

Metal-organic frameworks (MOFs) are an emerging class of materials which have garnered increasing attention for their utility as adsorbents and photocatalysts in water treatment. Nevertheless, the environmental risks of MOFs, especially their underlying impacts on aquatic organisms, are not fully explored. Herein, the toxicity of multiple representative MOFs was systematically assessed using a freshwater green alga (Chlamydomonas reinhardtii) model. Six typical MOFs with different metal nodes or organic linkers, including four transition metal incorporated aluminum-based porphyrin MOFs [pristine Al-PMOF, Al-PMOF (Cu), Al-PMOF (Ni), and Al-PMOF (Co)], one amine-functionalized MOF NH₂-MIL-125 (Ti), and one bimetallic Hofmann MOF (NiCo-PYZ), were successfully synthesized and characterized. All the tested MOFs significantly reduced the chlorophyll content and inhibited the algal growth, with the most toxic materials being NiCo-PYZ and Al-PMOF (Cu). Distinct toxic mechanisms were observed for the tested MOFs. Metal ion release was the primary cause for algal toxicity induced by NiCo-PYZ. The algal toxicity induced by porphyrin MOFs could be explained by the combined effects of metal ion release and nutrient adsorption, agglomeration and physical interactions, and reactive oxygen species generation. NH₂-MIL-125 (Ti) showed higher stability and more biocompatibility than the other tested MOFs. MOFs concentrations with no harmful effects to algae can be taken as the threshold values for safe use and discharge of MOFs. The ecotoxicological risks of MOFs should be considered as the applied concentrations of MOFs at mg/mL levels in environmental remediation were much higher than the no harmful effect thresholds.

The exploitation of a new adsorbent with a high adsorption performance and recyclability is of great practical significance for the treatment of wastewater containing mercury ions. In this study, a novel membrane adsorbent was fabricated by blending MoS₂ nanosheets into a PVDF polymer matrix (P-PVDF/MoS₂) followed by non-solvent-induced phase conversion. This material was able to bind mercury ions and was not affected by the solution ionic strength, co-existing anions, or interfering heavy metal ions. The optimal pH range for mercury ion elimination was 4.5–6.0, and P-PVDF/MoS₂ exhibited a maximum adsorption capacity of 578 mg g⁻¹. The pseudo-second-order adsorption kinetics and Langmuir isotherm models best described the adsorption process. The adsorption mechanism was mainly monolayer chemisorption, for which the S groups were the major active sites. Furthermore, the membrane could be removed from the aqueous solution easily using tweezers, and the removal efficiency of mercury ions remained over 90% after ten cycles. This study suggests that the inexpensive and recyclable P-PVDF/MoS₂ membranes can be used for the efficient removal of heavy metal ions from wastewater at a large scale.

Pollutants in wastewater and exhaust gas bring out serious concerns to public health and the environment. Biochar can be developed as a sustainable adsorbent originating from abundant bio-wastes, such as agricultural waste, forestry residue, food waste and human waste. Here we highlight the state-of-the-art research progress on pyrochar and hydrochar for the sorption of pollutants (heavy metal, organics, gas, etc) in wastewater and exhaust gases. The adsorption performance of pyrochar and hydrochar are compared and discussed in-depth, including preparation procedures (carbonization and activation), sorption possible mechanisms, and physiochemical properties. Challenges and perspective for designing efficient and environmental benign biochar-based adsorbents are finally addressed.

The presence of higher concentrations of heavy metals in water affects its quality with a concomitant adverse effect on its users thus their removal is paramount. A novel adsorbent, PN-Fe₃O₄-IDA derived from the chemical modification of peanut husk (a low-cost agricultural biomass produced in significant quantities globally) using magnetic nanoparticles (Fe₃O₄) and iminodiacetic acid was utilized for the remediation of heavy metals in aqueous solution. Analytical techniques vis-à-vis the Fourier-Transform Infrared, Scanning Electron Microscope, Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy and X-ray Diffraction were applied for the characterization of PN-Fe₃O₄-IDA. Results from the characterization studies showed that PN-Fe₃O₄-IDA possessed a mesoporous structure, a heterogeneous surface and functional groups such as carboxylic acid and a tertiary nitrogen atom which enhanced its adsorption capacities as well as magnetic properties which ensured its easy removal from the solution using a magnet. The maximum uptake of Pb and Cu onto PN-Fe₃O₄-IDA was 0.36 and 0.75 mmol g⁻¹ (at 318 K) respectively with the chemisorption process being the major reaction pathway for the processes. The synthesized adsorbent exhibits significant adsorption capacity for the selected pollutants as well as some unique features which promotes its use as an adsorbent for wastewater remediation processes.