A bifunctional adsorbent of silica gel-immobilized Schiff base derivative for simultaneous and selective adsorption of Cu(II) and SO42−

Recent advances in chitosan-based nanocomposites for adsorption and removal of heavy metal ions

Due to the high concentration of various toxic and dangerous pollutants, industrial effluents have imposed increasing threats. Among the various processes for wastewater treatment, adsorption is widely used due to its simplicity, good treatment efficiency, availability of a wide range of adsorbents, and cost-effectiveness. Chitosan (CS) has received great attention as a pollutant adsorbent due to its low cost and many -OH and -NH2 functional groups that can bind heavy metal ions. However, weaknesses such as sensitivity to pH, low thermal stability and low mechanical strength, limit the application of CS in wastewater treatment. The modification of these functional groups can improve its performance via cross-linking and grafting agents. The porosity and specific surface area of CS in powder form are not ideal, so physical modification of CS via integration with other materials (e.g., metal oxide, zeolite, clay, etc.) leads to the creation of composite materials with improved absorption performance. This review provides reports on the application of CS and its nanocomposites (NCs) for the removal of various heavy metal ions. Synthesis strategy, adsorption mechanism and influencing factors on sorbents for heavy metals are discussed in detail.

Adsorptive removal of heavy metals from wastewater using Cobalt-diphenylamine (Co-DPA) complex

Heavy metals like Cadmium, Lead, and Chromium are the pollutants emitted into the environment through industrial development. In this work, a new diphenylamine coordinated cobalt complex (Co-DPA) has been synthesized and tested for its efficiency in removing heavy metals from wastewater, and its adsorption capacity was investigated. The effectiveness of heavy metals removal by Co-DPA was evaluated by adjusting the adsorption parameters, such as adsorbent dose, pH, initial metals concentration, and adsorption period. Heavy metal concentrations in real sample were 0.267, 0.075, and 0.125 mg/L for Cd2+, Pb2+, and Cr3+ before using as-synthesized Co-DPA to treat wastewater. After being treated with synthesized Co-DPA the concentration of heavy metals was reduced to 0.0129, 0.00028, 0.00054 mg/L for Cd2+, Pb2+, and Cr3+, respectively, in 80 min. The removal efficiency was 95.6%, 99.5%, and 99.5% for the respective metals. The adsorption process fitted satisfactorily with Freundlich isotherm with R2(0.999, 0.997, 0.995) for Cd2+, Pb2+, and Cr3+, respectively. The kinetic data obeyed the pseudo-second order for Cd2+ and Cr2+ and the pseudo-first order for Pb2+. Based on the results obtained within the framework of this study, it is concluded that the as-synthesized Co-DPA is a good adsorbent to eliminate heavy metal ions like Cd2+, Pb2+, and Cr3+from wastewater solution. In general, Co-DPA is a promising new material for the removal of heavy metal ions from water.

Uptake of Ethyl Xanthate to Metal Organic Frameworks

As the mining industry spreads to new areas in the arctic regions, the need for re-useable efficient methods for mine chemicals' recycling increases. Especially in the case of xanthates, which are used as collectors for many metals from ore. Xanthates are very toxic to aquatic life either directly or indirectly and cause potentially severe health problems to humans after long-term exposure. In the present work, potassium ethyl xanthate (KEX) was observed to coordinate into metal organic frameworks (MOFs). HKUST-1 and its post-synthetically modified forms were observed to behave most effectively of the studied MOFs at low concentrations of KEX. Differences in the uptake of KEX were detected regarding the synthesis method in the case of MIL-100(Fe) synthetized by solvothermal and mechanochemical methods. Other studied MOFs, UiO-66 and MIL-100(Al)/MIL-96(Al), were not observed to be effective in KEX uptake.

Stability, Stimuli-Responsiveness, and Versatile Sorption Properties of a Dynamic Covalent Acylhydrazone Gel

Gel adsorbents are promising for pollutant removal from the wastewater. Herein, an acylhydrazone gel is developed from acylhydrazide-terminated pentaerythritol (PAT) and 2,4,6-triformylphloroglucinol (TFP) based on dynamic covalent acylhydrazone chemistry. PAT-TFP gel is stable under various conditions, while it shows reversible Cu2+ adsorption and desorption. PAT-TFP gel is studied as a versatile adsorbent for the capture of a range of (bulky) organic contaminants and heavy metal ions from aqueous solutions. Fast and good adsorption capacities are achieved for various dyes (rhodamine B and methyl orange), amines (aniline, p-chloroaniline, 4-methylaniline, and p-aminobenzoic acid), phenols (phenol, 1-naphthol, p-methylphenol, and bisphenol A), and metal ions (Cu2+, Cr3+, and Hg2+). The maximum adsorption capacity is 107.5 mg g-1 for Cu2+ and the equilibrium adsorption time is 30 min. PAT-TFP gel can be regenerated efficiently and used repeatedly.

Insight into the Synergistic Effect on Selective Adsorption for Heavy Metal Ions by a Polypyrrole/TiO2 Composite

Polymer/metal oxide composites are promising candidates for the treatment of water pollution. Adsorption selectivity as well as a large adsorption capacity are two key factors for treating wastewater containing multiple ions. Herein, a PPy⁺/TiO₂(O^-) composite with a heterojunction structure was first discovered to have novel selectivity toward heavy metal ions. An interesting self-doping nature of TiO₂(O^-) together with SO₄^2- for PPy⁺ was reported. This interesting structure contributed to an impressive selective adsorption capability with an ascending order of Zn²⁺ > Pb²⁺ ≫ Cu²⁺ in a ternary ion system, where the adsorption for Cu²⁺ could be almost suppressed. Through the designed adsorption experiments and characterization techniques including Fourier transform infrared, thermogravimetric analysis, and X-ray photoelectron spectroscopy, a universal synergistic mechanism for PPy⁺/TiO₂(O^-) composite was first proposed and confirmed. The doping and dedoping of metal oxide (dopant) from the polymer dictates the adsorption selectivity, where the selectivity is determined by the interaction between TiO₂ and heavy metal ions. This work may provide some useful guidelines for designing adsorbents with selectivity toward specific heavy metal ions.