Due to the extensive application of pesticides and their hazardous effects on organisms, there is an urgent need to remove them effectively from wastewater. Metal-incorporated carbon-mineral composites (Ni/Mn-CMC and Ni/Fe-CMC) described in this paper can certainly be applied for this purpose. They were synthesized by combining mechanochemical and pyrolytic processes and their physicochemical properties were investigated using numerous methods (SEM-EDS, N2 adsorption/desorption, XRD, surface charge, FTIR). Adsorption capacity towards diuron and carboxin with and without impurities commonly detected in natural ecosystems, cadmium ions or arsenite, was measured. The obtained results indicated that Ni/Fe-CMC is more efficient adsorbent of pesticides due to its well-developed surface. It was able to bind 158.34 mg g-1 of diuron and 133.58 mg g-1 of carboxin in the solutions, where only one pesticide was present. In turn, these values for the Ni/Mn-CMC sample were 126.49 mg g-1 and 102.08 mg g-1, respectively. It should be noted that the composites maintained their high adsorption capacity in the multicomponent solutions, i.e., containing both pesticide and metal ions. Then, the maximum reduction in pesticide adsorption was only 8.36. Ni/Mn-CMC and Ni/Fe-CMC were successfully regenerated with ethanol without changing their structure and adsorption capacity. Also, the extracts from investigated materials did not have negative impact on plant growth. This confirmed suitability of carbon-mineral composites for repeated multiple use without toxic effects to organisms.

Layered double hydroxides (LDH) have been shown to be effective adsorbents, but their utility for the treatment of per- and polyfluoroalkyl substances (PFAS) in water has not been fully explored. In this study, the adsorption of 9 PFAS on hydrotalcite (HT), a type of LDH, was investigated using reaction solutions with environmentally relevant PFAS concentrations. The adsorption of individual PFAS by HT depended upon a range of factors, including the temperature used to pre-treat (i.e., calcine) the HT, aging conditions, and the presence of anions in the solution. HT calcined near 400 °C most effectively adsorbed PFAS, but its ability to adsorb PFAS was sensitive to storage conditions. The adsorption of CO2 and moisture from air, which likely resulted in the re-intercalation of CO32- into the interlayer regions of HT, was observed to reduce PFAS adsorption and may explain performance loss over time. The adsorption trend among 9 PFAS and the influence on this process by Cl-, NO3-, SO42-, and CO32- indicated that adsorption occurred via a combination of ion exchange, electrostatic attraction, and hydrophobic interactions, although the relative importance of each mechanism deserves further investigation. During this study, we also demonstrated for the first time that HT can be thermally regenerated at 400 °C without affecting its ability to adsorb PFOS and PFBA. Overall, our results suggest that HT may serve as an effective alternative for PFAS treatment.

A novel biomass-based magnetic nanoparticle (Fe3O4-P-CMC/PAMAM) was synthesized by crosslinking carboxymethyl chitosan (CMC) and poly(amidoamine) (PAMAM), followed by phosphorylation with the incorporation of magnetic ferric oxide nanoparticles. The characterization results verified the successful functionalization and structural integrity of the adsorbents with a surface area of ca. 43 m2/g. Batch adsorption experiments revealed that the adsorbent exhibited a maximum adsorption capacity of 1513.47 mg·g-1 for U(VI) at pH 5.5 and 298.15 K, with Fe3O4-P-CMC/G1.5-2 showing the highest affinity among the series. The adsorption kinetics adhered to a pseudo-second-order model (R2 = 0.99, qe,exp = 463.81 mg·g-1, k2 = 2.15×10-2 g·mg-1·min-1), indicating a chemically driven process. Thermodynamic analysis suggested that the adsorption was endothermic and spontaneous (ΔH° = 14.71 kJ·mol-1, ΔG° = -50.63 kJ·mol-1, 298. 15 K), with increasing adsorption capacity at higher temperatures. The adsorbent demonstrated significant selectivity for U(VI) in the presence of competing cations, with Fe3O4-P-CMC/G1.5-2 showing a high selectivity coefficient. The performed desorption and reusability tests indicated that the adsorbent could be effectively regenerated using 1M HCl, maintaining its adsorption capacity after five cycles. XPS analysis highlighted the role of phosphonate and amino groups in the complexation with uranyl ions, and validated the existence of bimodal U4f peaks at 380.1 eV and 390.1 eV belonging to U 4f7/2 and U 4f5/2. The results of this study underscore the promise of the developed adsorbent as an effective and selective material for the treatment of uranium-contaminated wastewater.

The adsorption process efficiently removes per- and polyfluoroalkyl substances (PFAS) from water, but managing exhausted adsorbents presents notable environmental and economic challenges. Conventional disposal methods, such as incineration, may reintroduce PFAS into the environment. Therefore, advanced regeneration techniques are imperative to prevent leaching during disposal and enhance sustainability and cost-effectiveness. This review critically evaluates thermal and chemical regeneration approaches for PFAS-laden adsorbents, elucidating their operational mechanisms, the influence of water quality parameters, and their inherent advantages and limitations. Thermal regeneration achieves notable desorption efficiencies, reaching up to 99% for activated carbon. However, it requires significant energy input and risks compromising the adsorbent\'s structural integrity, resulting in considerable mass loss (10-20%). In contrast, chemical regeneration presents a diverse efficiency landscape across different regenerants, including water, acidic/basic, salt, solvent, and multi-component solutions. Multi-component solutions demonstrate superior efficiency (>90%) compared to solvent-based solutions (12.50%), which, in turn, outperform salt (2.34%), acidic/basic (1.17%), and water (0.40%) regenerants. This hierarchical effectiveness underscores the nuanced nature of chemical regeneration, significantly influenced by factors such as regenerant composition, the molecular structure of PFAS, and the presence of organic co-contaminants. Exploring the conditional efficacy of thermal and chemical regeneration methods underscores the imperative of strategic selection based on specific types of PFAS and material properties. By emphasizing the limitations and potential of particular regeneration schemes and advocating for future research directions, such as exploring persulfate activation treatments, this review aims to catalyze the development of more effective regeneration processes. The ultimate goal is to ensure water quality and public health protection through environmentally sound solutions for PFAS remediation efforts.

Per- and polyfluoroalkyl substances (PFAS) are man-made organic compounds ubiquitously present in the environment. Due to their persistency and bioaccumulative nature, and because of increasingly stringent regulations of PFAS, their removal from the environment is necessary. Our initial study identified all-silica zeolite β as an alternative adsorbent with a high selectivity, affinity, and capacity for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) removal. Here, we study the influence of the PFAS chain length on the affinity and capacity of a novel material, all-silica zeolite β, showing that the *BEA zeolite is an ideal sorbent for the removal of PFAS with 8 carbons. The solution pH and the addition of cations or natural organic substances to the water matrix have minimal influence on PFOA/PFOS removal with the zeolite. Next, regeneration of a PFOS-loaded zeolite was assessed; besides thermal, solvent-driven regeneration of the zeolite is also possible, using well-selected combinations of non-noxious solvents. Lastly, continuous adsorption experiments show that zeolite can be used for larger-scale applications.

The potential of pyrolyzed Mytella falcata shells as an adsorbent for removing methylene blue dye molecules from aqueous solutions was investigated. The study found that the adsorbent produced at 600 °C of pyrolysis temperature, with an adsorbent mass of 0.5 g, particle diameter of 0.297-0.149 mm, and pH 12.0, demonstrated the highest dye molecule removal efficiency of 82.41%. The material\'s porosity was observed through scanning electron microscopy, which is favorable for adsorption, while Fourier-transform infrared spectroscopy and X-Ray diffraction analysis analyses confirmed the presence of calcium carbonate in the crystalline phases. The pseudo-second order model was found to be the best fit for the data, suggesting that the adsorption mechanism involves two steps: external diffusion and diffusion via the solid pores. The Redlich-Peterson isotherm model better represented the equilibrium data, and the methylene blue adsorption was found to be spontaneous, favorable, and endothermic. The hydrogen peroxide with UV oxidation was found to be the most efficient method of regeneration, with a regeneration percentage of 63% achieved using 600 mmol.L-1 of oxidizing agents. The results suggest that pyrolyzed Mytella falcata shells could serve as an ecologically viable adsorbent alternative, reducing the amount of waste produced in the local environment and at the same time removing pollutants from the water. The material\'s adsorption capacity remained almost constant in the first adsorption-oxidation cycles, indicating its potential for repeated use.

Industrial wastewater is the main source of an excessive amount of molybdenum (Mo) in natural ecosystems. It is necessary to remove Mo from wastewater before it is discharged into the environment. Molybdate ion(VI) is the most common form of Mo in natural reservoirs and industrial wastewater. In this work, the sorption removal of Mo(VI) from an aqueous medium was evaluated using aluminum oxide. The influence of such factors as the pH of the solution and the temperature was evaluated. Three adsorption isotherms, namely, Langmuir, Freundlich and Temkin, were used to describe the experimental results. It was found that the pseudo-first order kinetic model better fits the kinetic data of the adsorption process, and the maximum Mo(VI) adsorption capacity was 31 mg/g at 25 °C and pH 4. The thermodynamic parameters indicated that the process of Mo(VI) adsorption on Al2O3 was exothermic and spontaneous. It was shown that the adsorption of Mo strongly depends on pH. The most effective adsorption was observed at pH values below 7. Experiments on adsorbent regeneration showed that Mo(VI) can be effectively desorbed from the aluminum oxide surface into a phosphate solution in a wide range of pH values. After the desorption of Mo(VI) in a phosphate solution, alumina was found to be suitable for repeating the procedure at least five times.

Imperative decarbonization of water purification processes entails alternative regeneration methods for activated carbon. Regeneration based on changing dissociation equilibria, i.e. a major influencing factor on adsorption, usually requires the addition of acids/bases, but may also be triggered by temperature swing. Although adsorption and dissociation are both temperature-dependent phenomena, their conjunction has received little attention regarding trace organic compounds (TrOCs) and large temperature intervals, in particular above ΔT ≥ 50 ∘C. Therefore, we studied the adsorption equilibria of 16 TrOCs onto one granular activated carbon at temperatures ranging from 20 to 95 ∘C. The majority of compounds (12/16) exhibited an exothermic apparent adsorption enthalpy, while 3 out of 16 exhibited an endothermic apparent enthalpy. The range spanned from - 46 to + 50 kJ mol-1 (median at - 17 kJ mol-1). The possible origins of endothermic adsorption were discussed. A rationale of shifting pKa and thus changing dissociation of TrOCs was introduced and traded off against existing rationales, i.e. changing solute solubility, changing adsorption heat capacity, and saturation effects of the adsorbates. This knowledge may allow designing temperature swing adsorption processes that unlock the dissociation switch. The augmented process efficiency can thus provide the foundation for low-carbon emission, circular water purification processes.

As interest in improving indoor air quality has increased, the development of long-lasting adsorbents that effectively and economically remove volatile organic compounds (VOCs) has become critical. In this study, TiO2-bearing activated carbon is introduced as a photocatalytic adsorbent in a renewable VOC filter. The activated carbon filter bearing TiO2 particles is prepared using the sol-gel method, followed by a spraying method. VOC adsorption and photocatalytic activity of the TiO2-bearing activated carbon are analyzed using a Tedlar bag sampling technique, using toluene and acetaldehyde as sample of VOC gas. Under ultraviolet-C (UV-C) irradiation for 22 h, the photocatalytic activity of TiO2 regenerates the VOC filters by 99 %. In addition, under UV-A and light-emitting diode, the TiO2-bearing activated carbon filters are regenerated by 60 % and 58 %, respectively, after 22 h. This result establishes its practical applicability as a renewable indoor VOC filter.

Chitosan (Cs)-based composites were developed by incorporating silica (Cs-Si), and both silica and hydroxyapatite (Cs-Si-Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs-Si and Cs-Si-Hap composite. Morphological images exhibits homogeneous Cs-Si surface, decorated with SiO2 nanoparticles, while the Cs-Si-Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs-Si-Hap was 10 min, comparatively better than Cs and Cs-Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs-Si, and Cs-Si-Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.