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Recently, removal of nickel ions has been gaining a lot of attention because of the negative impact of nickel ions on the environment. The aim of this review paper is to organize the scattered available information on removal of nickel ions from aqueous solutions through the adsorption process. Survey on investigated materials suggests that composite- and polymer-based adsorbents have the most effective capability for nickel adsorption. The composite material class, i.e. CaCO3-maltose, followed by biopolymer-based material showed the highest Ni(II) adsorption capacity of 769.23 and 500 mg/g, respectively. The importance of treatment parameters (i.e. pH, temperature, contact time, and metal ion concentration) is discussed, together with their effect on the underlying physicochemical phenomena, giving particular attention to the adsorption/desorption mechanism. It was ascertained that adsorption of nickel ions is pH dependent and the optimal pH range for adsorption of Ni(II) ions was in range of 6–8. In general, nickel adsorption is an endothermic and spontaneous process that mainly occurs by forming a monolayer on the adsorbent (experimental data are often fitted by Langmuir isotherms and pseudo-second-order kinetics). Regeneration (i.e. desorption) is also reviewed, suggesting that acidic eluents (e.g. HCl and HNO3) allow, in most of the cases, an efficacious spent adsorbent recovery. The percentage use of desorption agents followed the order of acids (77%) > chelators (8.5%) > alkalis (8%) > salts (4.5%) > water (2%). Helpful information about adsorption and desorption of nickel ions from aqueous solutions is provided. [ABSTRACT FROM AUTHOR]

• Regeneration of chitosan adsorbents after heavy metal adsorption is reviewed. • Desorption ability of different desorption agents is summarized. • Desorption mechanism of heavy metal ions from chitosan-based adsorbents is described. • Factors affecting regeneration of chitosan adsorbents are highlighted. Adsorption of heavy metal ions on chitosan-based adsorbents has been extensively investigated. However, few studies explored the feasibility of desorbing and regenerating chitosan. Adsorbents used after adsorption of heavy metals are discarded, and this practice exacerbates the solid treatment problem. Regeneration and reuse of exhausted adsorbents should be considered to operate environment-friendly and cost-effective adsorption. This review was performed to summarize the desorption of heavy metal ions and possible regeneration of chitosan-based adsorbents using various desorption agents such as acids, alkalis, salts, and chelating agents. It was found that the highest desorption efficiencies obtained by acidic eluents. The percentage use of desorption agents for desorbing followed the order of acids (49.3%) > chelators (26.9%) > alkalis (14.9%) > salts (8.9%). Moreover, the proper desorption time were estimated to be 0.84 by 1.37 h. Beneficial information is provided for regeneration and recovery of chitosan adsorbents. [ABSTRACT FROM AUTHOR]

Chitosan and its derivatives are effective for adsorbing dye molecules from aqueous solutions. However, their use can be limited by environmental concerns on their fate after adsorbent saturation. Desorbing dye molecules and regenerating adsorbents are alternatives to disposing spent adsorbent. In this review, most research topics related to regenerating chitosan-based adsorbents for dye removal are summarized and discussed. Numerous desorption agents, such as acids, alkalis, salts, and organic solvents, have been applied to regenerate chitosan-based adsorbents and recover the adsorbed dye molecules. In addition, the mechanism of desorbing dye molecules from these adsorbents is examined to provide information on selecting methods for recovering chitosan-based adsorbents. [ABSTRACT FROM AUTHOR]

In this study, hexadecylamine (HDA) impregnated chitosan-powder activated carbon (Ct-PAC) composite beads were successfully prepared and applied to adsorption of the anionic dye reactive black 5 (RB5) in aqueous solution. The Ct-PAC-HDA beads synthesized with 0.2 g powdered activated carbon (PAC) and 0.04 g HDA showed the highest dye removal efficiency. The prepared beads were characterized using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Various adsorption parameters, i.e., adsorbent dosage, pH, and contact time, which affect the adsorption performance, were studied in a series of batch experiments. The obtained adsorption data were found to be better represented by Freundlich (R2 = 0.994) and pseudo-second-order (R2 = 0.994) models. Moreover, it was ascertained that the adsorption of RB5 onto Ct-PAC-HDA beads is pH-dependent, and the maximum Langmuir adsorption capacity (666.97 mg/g) was observed at pH 4. It was also proved that Ct-PAC-HDA beads were regenerable for repeated use in the adsorption process. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • ZrO(OH) 2 nanoparticles with the size of 5–20 nm are loaded in the vermiculite. • ZrO(OH) 2 /VMT shows a high adsorption capacity of 90.21 mg/g for Ni(II). • ZrO(OH) 2 /VMT exhibits excellent stability in acidic solution (pH > 1.5). • ZrO(OH) 2 /VMT is favorable for Ni(II) removal from electroplating wastewater. • The spent ZrO(OH) 2 /VMT can be successfully regenerated and reused. Abstract Novel vermiculite-based hydrated zirconium oxide (ZrO(OH) 2 /VMT) nanocomposites were synthesized via a simple ion exchange-precipitation method and applied to remove Ni(II) from aqueous solution. After ZrO(OH) 2 particles in the size range of 5–20 nm were loaded in the vermiculite (VMT), the prepared ZrO(OH) 2 /VMT had a lamellar structure with a high specific surface area of 130.86 m2/g. The ZrO(OH) 2 /VMT adsorbent exhibited excellent stability in acidic solution. Adsorption equilibrium of Ni(II) was reached within 120 min, and the maximum Ni(II) adsorption capacity on ZrO(OH) 2 /VMT was 90.21 mg/g according to the Langmuir fitting, higher than most of the reported adsorbents. The adsorbed amounts of Ni(II) on the ZrO(OH) 2 /VMT increased with increasing solution pH from 2 to 8. The real electroplating wastewaters was employed to evaluate the adsorption of Ni(II) on the ZrO(OH) 2 /VMT in the column experiments, and about 402 bed volumes of wastewater could be treated before the concentrations of Ni(II) in effluent reached 0.1 mg/L. In addition, the spent ZrO(OH) 2 /VMT could be successfully regenerated in 0.04 mol/L HCl solution, and the ZrO(OH) 2 /VMT exhibited stable adsorption for Ni(II) in the five successive adsorption cycles. [ABSTRACT FROM AUTHOR]

The regeneration of Fischer-Tropsch (FT) catalysts plays a crucial role in sustaining their catalytic activity and longevity in sustainable production processes. This research investigates the effectiveness of various solvents, including n-hexane, n-heptane, toluene, xylene, and the liquid fraction of FT products (LF-FT), for catalyst regeneration and extracting wax from the 15 wt%Co/Al 2 O 3 catalyst. Toluene, with a unique combination of key parameters such as polarity, solubility, boiling point, aromatic structure, and chemical interactions, exhibited the highest wax removal efficiency of 90.6%. However, due to its 41 °C lower boiling point compared to toluene and very similar wax removal efficiency, n-hexane appears as a more energy-efficient and cost-effective option for this process. The regenerated catalysts showed comparable characteristics, including the textural properties (surface area, pore size, and pore volume), crystallinity, and reducibility, to fresh catalysts. The slightly lower reduction temperature in the regenerated catalyst indicates a higher possibility for the formation of cobalt active sites during the catalyst reduction process with hydrogen, leading to an increased potential for higher catalytic activity. The LF-FT, comprising paraffins, iso-paraffins, olefins, napthenes, and aromatics, provided a unique combination of aliphatic and aromatic moieties, enhancing the solubility of both polar and nonpolar components in FT wax and improving the wax removal efficiency to 91.5%. The higher boiling point and operating temperature of the LF-FT also contributed to its better performance. Efficient separation of hydrocarbons from solvents allowed for solvent reusability in subsequent FT wax removal cycles, making it advantageous for large-scale applications. [Display omitted] • Different solvents (n-hexane, toluene, n-heptane, xylene, LF-FT) assessed for FT catalyst regeneration. • Toluene displayed the highest wax removal efficiency, followed by n-hexane, n-heptane, and xylene. • N-hexane emerges as optimal solvent with low boiling point, cost-effective, and energy-efficient for wax extraction.. • Regenerated catalysts matched fresh ones, indicating restored surface properties and accessible cobalt active sites. • LF-FT solvent, with aliphatic and aromatic components, shows promise for FT catalyst regeneration with enhanced solubility. [ABSTRACT FROM AUTHOR]

Regeneration and reuse of spent activated carbon (AC) as well as recovery of the desorbed pollutants are challenging in the application of adsorption technology. In this study, the regeneration of perfluorooctanesulfonate (PFOS)-saturated coal-based granular AC by hot water and subsequent aeration method to enrich PFOS from eluent were investigated. The regeneration time, water temperature and solid-liquid ratio affected the regeneration efficiency of PFOS treated AC. PFOS was desorbed quickly from the AC within 30 min by hot water. High water temperature (92 °C) and low solid-liquid ratio (0.5) led to the highest desorption of 36.7% in one cycle (6 h). Over 90% PFOS on the spent AC was desorbed by 92 °C hot water with the solid-liquid ratio of 0.5 after six cycles. Subsequent experiments were conducted to enrich PFOS, and aeration of the regeneration eluent achieved the enrichment factors of 50.6–62.0 for PFOS at initial PFOS concentrations of 10–100 μg/L. The concentration of PFOS in the concentrated solution was 2.2 g/L following sequential sorption, regeneration and aeration treatments when the influent PFOS concentration was 2.7 μg/L. [ABSTRACT FROM AUTHOR]

Trichloropropyl phosphate (TCPP) as a widely used typical chlorinated organophosphate flame retardant has received significant attention because of its widespread presence in water and negative effects on human health. In this study, a ball-milling method was used to prepare a magnetic powdered carbon adsorbent (PC/nano-Fe 3 O 4 composite) for TCPP removal via adsorption and catalytic degradation. The effect of Fe 3 O 4 content on TCPP adsorption and degradation performance by PC/nano-Fe 3 O 4 composite was investigated. The PC/nano-Fe 3 O 4 composite prepared by high Fe 3 O 4 content (25%) was not favorable for TCPP adsorption and degradation. However, the PC/Fe 3 O 4 containing low Fe 3 O 4 content (10%) had insufficient magnetic separation ability from water. The synthesized PC/nano-Fe 3 O 4 composite with a Fe 3 O 4 /PC mass ratio of 1/5 exhibited a maximum adsorption capacity of 2682.1 μg/g as well as a complete TCPP degradation within 3 h in a Fenton-like system. Moreover, the possible break sites of TCPP and its degradation pathway were proposed based on theoretical calculation and experimental analysis. Regeneration studies showed that PC/nano-Fe 3 O 4 composite had high reusability and adsorption capacity in six cycles, while its catalytic performance declined in the multiple reuse cycles. This strategy could be extended to prepare other magnetic powdered adsorbents for organic pollutant adsorption and degradation. [Display omitted] • Magnetic PC/nano-Fe 3 O 4 composite was successfully synthesized by a simple ball-milling method. • PC/nano-Fe 3 O 4 composite showed a high adsorption capacity of 2682.1 μg/g for TCPP. • PC/nano-Fe 3 O 4 composite can be used as a catalyst to completely degrade TCPP in a Fenton-like system. • TCPP degradation pathway was proposed based on DFT calculation and experimental analysis. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) with great application potential in environmental remediation exist as the form of powder, which are difficult to separate and recycle. Two magnetic COFs with good recyclability were prepared through simple impregnation-precipitation method in this study. The prepared magnetic COFs were used for the adsorptive removal of diclofenac sodium (DCF). The introduction of hydroxyl group on magnetic COF (OH-MCOF) could greatly enhance its adsorption amount for DCF, and OH-MCOF was selected to study the effect of adsorption time, initial concentrations, solution pH and ionic strength on its adsorption for DCF, as well as its regeneration and reuse performance were investigated. In this study, the OH-MCOF had a high adsorption capacity for DCF of 203.4 mg/g based on the Langmuir model fitting, and exhibited quickly adsorption for DCF within 30 min. The adsorption efficiency was better than that of most reported adsorbents. Furthermore, the role of hydroxyl group on magnetic COF was highlighted through density functional theory (DFT) and electrostatic potential (ESP) calculation. After 5 cycles of regeneration, the OH-MCOF still maintained the same adsorption amount for DCF, showing good reusability and stability. This study reveals OH-MCOF with high removal and reusability in the further application of environmental remediation. [ABSTRACT FROM AUTHOR]