Removal of Cr(VI) from aqueous solution by a novel ZnO-sludge biochar composite

Synthesis of poly (acrylic acid) modified graphene/MoS2 heterostructure-based composite: an effective removal of Pb(II), Cd(II) and Zn(II) from wastewater

Heavy metal contaminants have attracted widespread attention due to their severe toxicity and bioaccumulation. In this study, a novel graphene (EG)/molybdenum disulfide (MoS2) modified with poly (acrylic acid) (PAA) composites (EG/MoS2/PAA) were successfully synthesized via a one-step hydrothermal method and effectively removed Pb(II), Zn(II), and Cd(II) ions from wastewater. The incorporation of PAA within the EG/MoS2 significantly improved sorption ability. The EG/MoS2/PAA composite was characterized using XRD, FTIR, TEM, Raman, SEM-EDS, EIS, and cyclic voltammetry, which confirmed the successful synthesis of the EG/MoS2/PAA composite. The adsorption isotherm and kinetic of Pb(II), Zn(II), and Cd(II) were fitted with the Temkin isotherm and pseudo-second-order model, respectively. The maximum adsorption capacities (qmax) obtained using the Langmuir model were 47.13 mg/g for Pb(II) at pH 5, while 12.59 and 12.89 mg/g for Zn(II) and Cd(II) at pH 7. In the presence of interfering cations (i.e., Na+, Cu2+, Co2+, Fe3+, and Mg2+), the EG/MoS2/PAA adsorbent exhibited high selectivity and excellent reusability after three cycles. The adsorption mechanism of Pb(II), Zn(II), and Cd(II) onto the EG/MoS2/PAA composite surface was found to be primarily controlled by complexation and electrostatic interaction. This novel EG/MoS2/PAA adsorbent has excellent suitability for practical application in the treatment of highly contaminated wastewater.

Removal of Cr(vi) in wastewater by Fe-Mn oxide loaded sludge biochar

Sludge biochar loaded with Fe-Mn oxides (FMBC) was prepared and employed to remove Cr(vi) from wastewater. The influences of solution pH, co-existing ion, contact time, adsorption temperature and Cd(vi) concentrations on removing Cr(vi) by FMBC were investigated. The Cr(vi) adsorption on FMBC had strong pH dependence. Additionally, Na+, Mg2+, Ca2+, SiO32-, NO3- and Cl- ions exhibited no influence on Cr(vi) removal efficiency for FMBC, whereas there were inhibition effects of Pb2+, Cu2+, Ni2+, CO32-, SO42-, and PO43- on removing Cr(vi). The Cr(vi) adsorption from solution for FMBC was well described by models of pseudo-second-order and Langmuir, and the largest Cr(vi) removal capacity of FMBC reached 172.3 mg g-1. FMBC had good capacity for treating electroplating wastewater and mineral dissolving wastewater containing Cr(vi). After five regenerations, the 50 and 5 mg L-1 Cr(vi) removing efficiency of FMBC was 82.34% and 97.68%, respectively. The Cr(vi) removal for FMBC involved adsorption-reduction and re-adsorption of Cr(iii) generated by reduction. These results indicated that FMBC has good prospects for remediating Cr(vi)-containing wastewater.

Preparation of a novel polypyrrole/dolomite composite adsorbent for efficient removal of Cr(VI) from aqueous solution

A novel adsorbent, deposited PPy on the DMI (PPy/DMI) composite, was successfully synthesized for Cr(VI) removal from aqueous solution. PPy/DMI composite was characterized by BET, SEM, TEM, XRD, and XPS. The SEM and TEM analyses revealed that DMI can greatly reduce the aggregation of PPy and significantly enhance its adsorption performance. The Cr(VI) removal was highly pH dependent. The high selectivity of PPy/DMI composite for Cr(VI) removal was found even in the presence of co-existing ions. The adsorption kinetic process followed the pseudo-second-order equation, demonstrating that the Cr(VI) adsorption behavior onto PPy/DMI is chemisorption. Furthermore, the intra-particle diffusion model implied that the adsorption was controlled by both liquid membrane diffusion and internal diffusion. The adsorption isotherm data fitted well with the Langmuir model with the maximum adsorption capacity (406.50 mg/g at 323 K) which was considerably higher than that of other PPy-based adsorbents. The Cr(VI) adsorption onto PPy/DMI composite was endothermic. The main mechanisms of Cr(VI) removal are involved in adsorption through electrostatic attractions, ion exchange, and in situ reduction. The results suggested that PPy/DMI composite could be a promising candidate for efficient Cr(VI) removal from aqueous solution.

Removal of Chromium Species by Adsorption: Fundamental Principles, Newly Developed Adsorbents and Future Perspectives

Emerging chromium (Cr) species have attracted increasing concern. A majority of Cr species, especially hexavalent chromium (Cr(VI)), could lead to lethal effects on human beings, animals, and aquatic lives even at low concentrations. One of the conventional water-treatment methodologies, adsorption, could remove these toxic Cr species efficiently. Additionally, adsorption possesses many advantages, such as being cost-saving, easy to implement, highly efficient and facile to design. Previous research has shown that the application of different adsorbents, such as carbon nanotubes (carbon nanotubes (CNTs) and graphene oxide (GO) and its derivatives), activated carbons (ACs), biochars (BCs), metal-based composites, polymers and others, is being used for Cr species removal from contaminated water and wastewater. The research progress and application of adsorption for Cr removal in recent years are reviewed, the mechanisms of adsorption are also discussed and the development trend of Cr treatment by adsorption is proposed.