The oxidative degradation of polystyrene resins on the removal of Cr(VI) from wastewater by anion exchange

Using polyacrylamide hydrogel to adsorb chloride ions in cement-based materials

Concrete material is an important engineering material for modern marine engineering construction, but the presence of chloride ions in sea sand and seawater can cause corrosion of reinforcing steel, which greatly endangers the safety of reinforced concrete structures. Gel is an environmental friendly functional material which has the functions of exchange and adsorption of ions. Therefore, in this paper, polyacrylamide (PAM) gels were prepared for chloride ions adsorption in a reinforced concrete system. The chloride ions adsorption behavior of PAM gel in simulated seawater and cement were investigated and the maximum adsorption capacity of chloride ions in simulated seawater was 32.67 mg g-1. In addition, compared with the cement sample without gel, the chloride ion content in the cement sample containing 1.5 wt% gel was reduced 46.8% at a depth of 0-2.5 mm from the sample's surface. The results showed that PAM gel can effectively adsorb the chloride ion and improve the chloride ion penetration resistance in cement because the three-dimensional network structure of PAM gels allowed chloride ions to enter the inside of the gel. This gel has potential applications in the field of marine construction.

Removal performance and mechanism of poly(N1,N1,N3,N3-tetraallylpropane-1,3-diaminium chloride) toward Cr(VI)

The adsorption characteristic and mechanism of poly(N¹,N¹,N³,N³-tetraallylpropane-1,3-diaminium chloride) (PTAPDAC) toward Cr(VI) ions were systematically investigated. Results showed that the removal efficiency of PTAPDAC toward Cr(VI) could reach above 98% at pH = 3-6. The equilibrium data of Cr(VI) adsorbed by PTAPDAC fitted the Langmuir model well, and the maximum sorption capacity deduced from the Langmuir model at 293 K was 273.17 mg g^-1. The adsorption of PTAPDAC toward Cr(VI) was rapid and reached equilibrium within 60 min, and the adsorption kinetic process was relevant to the pseudo-second-order kinetic model. Moreover, the activation energy E _a was calculated as -22.505 kJ mol^-1. The adsorption processes were spontaneous and exothermic driven by an increase in entropy, which involved electrostatic attraction, ion exchange, and redox reactions. The X-ray photoelectron spectroscopy analysis revealed that approximately 64.5% of Cr(VI) reduced to be Cr(III), and 24.29% of -C-NH⁺ deprotonated. The combination of reduced Cr(III) with tertiary amine groups resulted in a positively charged tertiary amine group, which further promoted Cr(VI) adsorption, thereby increasing the adsorption capacity of PTAPDAC toward Cr(VI). Therefore, PTAPDAC has a broad application prospect in removing Cr(VI) ions in wastewater.

A multiple model approach for evaluating the performance of time-lapse capsules in trapping heavy metals from water bodies

This article applies multiple approaches for evaluating the effect of operating factors on the adsorption of heavy metals from watershed using time-lapse capsules.

Preparation, characterization and performance of an electrospun carbon nanofiber mat applied in hexavalent chromium removal from aqueous solution

Hexavalent chromium, Cr(VI), a highly toxic oxyanion known as a carcinogen and mutagen, is an issue of concern due to its adverse impact on human health. Therefore, development of effective technologies and/or materials for Cr(VI) removal from water has been of great interest for researchers. In this study, an electrospun carbon nanofiber (CNF) mat was prepared via electrospinning polyacrylonitrile (PAN), followed by thermal pre-oxidation and carbonization. Scanning electron microscopy (SEM) observation showed that the fiber diameter of the CNF with carbonization temperature of 950°C (CNF₉₅₀) was about 266 nm. Potentiometric titration analysis demonstrated that the point of zero charge pH (pH_pzc) of CNF₉₅₀ was around 7.93. CNF₉₅₀ demonstrated high adsorption capacity and fast adsorption kinetics for Cr(VI) at pH < 3. Langmuir isotherm calculations showed that the maximum adsorption capacity of Cr(VI) on CNF₉₅₀ was 118.8 mg/g at pH 2. The adsorption isotherm of Cr(VI) on CNF₉₅₀ was well described by the Redlich-Peterson model, revealing that Cr(VI) adsorption was the result of a combination of monolayer and multilayer adsorption, depending on the initial Cr(VI) concentration. Solution pH greatly affected Cr(VI) adsorption onto CNF₉₅₀ due to the electrostatic interaction, and the adsorption capacity was relatively high when pH was below 3. X-ray photoelectron spectroscopy (XPS) analysis revealed that the removal of Cr(VI) might be the result of a combination of redox reaction and electrostatic adsorption. The adsorption-saturated CNF₉₅₀ could be regenerated by NaOH solution. This study extends the potential applicability of electrospun CNF mats for Cr(VI)-contaminated water purification.

Reusable and removable PmPD/PVA membrane for effective Cr(vi) adsorption and reduction

The PmPD/PVA membranes with facile reusability for and highly effective removal of Cr(vi).

Research on adsorption of Cr(Ⅵ) by Poly-epichlorohydrin-dimethylamine (EPIDMA) modified weakly basic anion exchange resin D301

A novel composite, EPIDMA/D301, with high adsorption capacity and particular affinity toward Cr(Ⅵ) was well prepared utilizing cationic polyelectrolyte poly-epichlorohydrin-dimethylamine (EPIDMA) impregnated in the networking pores of the styrene macroporous weak basic anion exchange resin D301. The physicochemical characteristics of EPIDMA/D301 were characterized by the Brunauer-Emmett-Teller (BET), zeta potential, FTIR, SEM-Mapping and XPS. The adsorption properties were researched via the influence of the concentration of EPIDMA, adsorbent dose, pH, the initial concentration of Cr(Ⅵ) solution, contact time and temperature. Results presented that the weakly basic anion exchange resin supported cationic polymer showed the excellent potential of removing Cr(VI) ions primarily due to the nonspecific Cr(VI) adsorption resulted from the polymeric host D301, the electrostatic attraction of amino groups fixed on the D301 matrix and the embedded EPIDMA with Cr(VI) ions and the ion exchange by the displacement of Cl^- mainly derived from EPIDMA with Cr(VI) ions. The kinetic data were best fitted by the pseudo-second-order kinetic model. The batch equilibrium data followed Langmuir isotherm model well with the maximum adsorption capacity of 194 mg g^-1 at 25 °C, which demonstrated that the styrene anion exchange resin modified with EPIDMA might be an efficient approach to eliminate potentially toxic metals.

A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism

Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms.

Simultaneous uptake of NOM and Microcystin-LR by anion exchange resins: Effect of inorganic ions and resin regeneration

This study investigated the efficiency of a strongly basic macroporous anion exchange resin for the co-removal of Microcystin-LR (MCLR) and natural organic matter (NOM) in waters affected by toxic algal blooms. Environmental factors influencing the uptake behavior included MCLR and resin concentrations, NOM and anionic species, specifically nitrate, sulphate and bicarbonate. A860 resin exhibited an excellent adsorption capacity of 3800 μg/g; more than 60% of the MCLR removal was achieved within 10 min with a resin dosage of 200 mg/L (∼1 mL/L). Further, kinetic studies revealed that the overall removal of MCLR is influenced by both external diffusion and intra-particle diffusion. Increasing NOM concentration resulted in a significant reduction of MCLR uptake, especially at lower resin dosages, where a competitive uptake between the charged NOM fractions and MCLR was observed due to limited active sites. In addition, MCLR uptake was significantly reduced in the presence of sulphate and nitrate in the water matrix. Moreover, performance of the resin proved to be stable from one regeneration cycle to another. Approximately 80% of MCLR and 50% of dissolved organic carbon (DOC) were recovered in the regenerated brine. Evidences of resin saturation and site reduction were also observed after 2000 bed volumes (BV) of operation. For all the investigated water matrices, a resin dosage of 1000 mg/L (∼4.5 mL/L) was sufficient to lower MCLR concentration from 100 μg/L to below the World Health Organization guideline of 1 μg/L, while simultaneously providing more than 80% NOM removal.

Abnormal adsorption and desorption behavior of pharmaceutical drugs on polystyrene microspheres

We report an abnormal adsorption and desorption behavior where a stronger adsorption interaction between polystyrene particles and pharmaceutical drugs results in preferable desorption behavior.