Polymeric hydrogels-based materials for wastewater treatment

Low-cost and reliable wastewater treatment is a relevant issue worldwide to reduce the concentration of environmental pollutants. Industrial effluents containing dyes, heavy metals, and other inorganic and organic compounds can pollute water resources; therefore, novel technologies are required to mitigate and control their release into the environment. Adsorption is one of the simplest methods for treating contaminated water in which a wide spectrum of adsorbents can be used to remove emerging compounds. Hydrogels are interesting materials with high adsorption capacities that can be synthesized via green routes. These adsorbents are promising for large-scale industrial wastewater treatment applications; however, gaps still exist in achieving sustainable commercial implementation. This review focuses on the discussion and analysis of preparation, characterization, and adsorption properties of hydrogels for water purification. The advantages of these polymeric materials for water treatment were analyzed, including their performance in the removal of different organic and inorganic contaminants. Recent advances in the functionalization of hydrogels and the synthesis of novel composites have also been described. The adsorption capacities of hydrogel-based adsorbents are higher than 500 mg/g for different organic and inorganic pollutants, and can reach values of up to >2000 mg/g for organic compounds, significantly outperforming other materials reported for water cleaning. The main interactions involved in the adsorption of water pollutants using hydrogel-based adsorbents were described and explained to allow the interpretation of their removal mechanisms. The current challenges in the implementation of hydrogels for water purification in real-life operations are also highlighted. This review provides an updated picture of hydrogels as interesting materials to address water depollution worldwide.

Superabsorbents and Their Application for Heavy Metal Ion Removal in the Presence of EDDS

Three acrylic-based superabsorbents—TerraHydrogel^®Aqua (THA), Zeba^®Hydrogel (ZH) and Agro^®Hydrogel (AH) were used to investigate the influence of chemical conditions on kinetic and adsorption behavior towards metal ions in the presence of a chelating agent of a new generation called ethylenediamine-N,N′-disuccinic acid (EDDS). The effects of relevant parameters—mainly including those of sorbent dose, pH of the solution and initial concentration of Cu(II), Zn(II), Mn(II) and Fe(III) complexes with EDDS as well as phase contact time and temperature—on the adsorption efficiency were studied in detail by the static method. The experimental data were also characterized by kinetic and adsorption parameters obtained based on the Langmuir and Freundlich models of sorption as well as the Lagergren, Ho and McKay and Weber–Morris models.

A Short Review on Recent Advances of Hydrogel-Based Adsorbents for Heavy Metal Ions

The growth of industry fulfills our necessity and promotes economic development. However, pollutants from such industries pollute water bodies which pose a high risk for living organisms. Thus, researchers have been urged to develop an efficient method to remove toxic heavy metal ions from water bodies. The adsorption method shows promising results for the removal of heavy metal ions and is easy to operate on a large scale, thus can be applied to practical applications. Numerous adsorbents were developed and reported, among them hydrogels, which attract great attention because of the reusability, ease of preparation, and handling. Hydrogels are generally prepared by the cross-linking of polymers that result in a three-dimensional structure, showing high porosity and high functionality. They are hydrophilic in nature because of the functional groups, and are non-toxic. Thus, this review provides various methods of hydrogel adsorbents preparation and summarizes recent progress in the use of hydrogel adsorbents for the removal of heavy metal ions. Further, the mechanism involved in the removal of heavy metal ions is briefly discussed. The most recent studies about the adsorption method for the treatment of heavy metal ions contaminated water are presented.

Novel polyacrylamide-based solid scale inhibitor

Novel solid-state phosphorus-containing polymer was synthesized, characterized and investigated as anti-scaling agent for the removal of alkaline earth metals ions from water. An optimization protocol for the sorption process of the metal ions on the polymer surface was proposed and executed. The protocol involved parameters such as pH, contact time, polymer dose, and the initial concentration of the metal ion. The optimum pH was found to be around seven for all of the tested metal ions. The maximum sorption capacities of the prepared polymer were 667, 794, 769 and 709 (mg/g) for Mg, Ca, Sr and Ba ions, respectively. Evaluation of the sorption process from the isotherm, kinetic and thermodynamic points of view was also studied. The experimental evidence revealed that the sorption obeys Langmuir isotherm model and follows a pseudo-second order mechanism. Moreover, the sorption process is exothermic. Possibility of polymer reuse was also investigated.

Sorption of zinc by novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid

Novel pH-sensitive hydrogels based on chitosan, itaconic acid and methacrylic acid were applied as adsorbents for the removal of Zn(2+) ions from aqueous solution. In batch tests, the influence of solution pH, contact time, initial metal ion concentration and temperature was examined. The sorption was found pH dependent, pH 5.5 being the optimum value. The adsorption process was well described by the pseudo-second order kinetic. The hydrogels were characterized by spectral (Fourier transform infrared-FTIR) and structural (SEM/EDX and atomic force microscopy-AFM) analyses. The surface topography changes were observed by atomic force microscopy, while the changes in surface composition were detected using phase imaging AFM. The negative values of free energy and enthalpy indicated that the adsorption is spontaneous and exothermic one. The best fitting isotherms were Langmuir and Redlich-Peterson and it was found that both linear and nonlinear methods were appropriate for obtaining the isotherm parameters. However, the increase of temperature leads to higher adsorption capacity, since swelling degree increased with temperature.

Characterization and adsorption mechanism of Zn2+ removal by PVA/EDTA resin in polluted water

Batch adsorption experiments were conducted using a PVA/EDTA resin as an adsorbent to adsorb Zn(II) ions from single component system in which experimental parameters were studied including solution pH, contact time, adsorbent dose and initial metal ions concentration. The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperatures. The results showed that the maximum removal of Zn(II) (99.8%) with 1 g L(-1) of sorbent was observed at 40 mg L(-1) at an initial pH value of 6. Removals of about 60-70% occurred in 15 min, and equilibrium was attained at around 30 min. The equilibrium data for the adsorption of Zn(II) on PVA/EDTA resin was tested with various adsorption isotherm models among which three models were found to be suitable for the Zn(II) adsorption. In addition, the kinetic adsorption fitted well to the pseudo-second-order model and the corresponding rate constants were obtained. Thermodynamic aspects of the adsorption process were also investigated. Furthermore a higher desorption efficiency of Zn(II) from the PVA/EDTA resin using acid treatment was available by more than 95%.