Functional graphene oxide for organic pollutants removal from wastewater: a mini review

Sludge-derived alginate-like extracellular polymers (ALE) for preparation of Fe-ALE and FeCaMg-ALE: Application to the adsorption of phosphate

Excess phosphorus (P) in wastewater has potential risk of causing harmful algal bloom and eutrophication in receiving wastewater. In this study, alginate-like extracellular polymers (ALE) derived from conventional activated sludge were modified with ionic cross-linking agents (Fe3+, Ca2+, and Mg2+) to develop Fe-ALE and FeCaMg-ALE for the adsorption of phosphate from wastewater. The adsorption process of phosphate by Fe-ALE and FeCaMg-ALE can be well described by pseudo-second-order kinetics and Freundlich isotherm model with a high level of accuracy, indicating that the adsorption processes were chemical, multi-layer adsorption process. The maximum adsorption capacity of dry Fe-ALE and FeCaMg-ALE concerning phosphate were 15.06 and 20.10 mg/g, respectively at 298 K. The adsorption capacity remained relatively consistent across a pH range of 2.0-11.0. FT-IR, XRD, SEM coupled with XPS analysis demonstrated the ALE had been successfully compounded with Fe3+ or Fe3+/Ca2+/Mg2+. Based on the experimental results and characteristic analysis, the main mechanism of phosphate by Fe-ALE and FeCaMg-ALE are physical filling, electrostatic attraction, ligand exchange and precipitation reaction. This work provides a new perspective for preparing ALE-based adsorbent using conventional activated sludge as raw material, realizing the treatment of waste with waste and effectively recovering phosphate from wastewater.

Facile hydrothermal assembly of three-dimensional GO-MTZE composite and its adsorption properties toward Cu2

Three-dimensional (3D) graphene oxide (GO)-based aerogels, GO and 4-methyl-5-thiazoleethanol (MTZE) composites, were prepared by a facile hydrothermal method. Due to the hydrogen bonding and π-π stacking interactions, the produced 3D GO-MTZE composites possessed large cylindrical structures. The morphologies, composition, and chemical states of 3D GO-MTZE3:1 composite were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and N2 adsorption-desorption isotherms based on the Brunauer-Emmett-Teller (BET) method. The existence of nitrogen (N)-containing heterocyclic system and oxygen (O)-containing branched chain of MTZE contributed to the formation of 3D structures, while the complexation effect of heterocyclic sulfur (S)- and N-containing functional groups of MTZE for metal cations dominated the adsorption performance of 3D GO-MTZE3:1 composite, which could selectively adsorb copper ions (Cu2+). In addition, the better hydrophobic property of 3D GO-MTZE3:1 composite facilitates its facile recycling from aqueous solution after adsorption. The adsorption data of 3D GO-MTZE3:1 composite toward Cu2+ fitted well (R2 = 0.9996) with the linear pseudo-second-order kinetic model, giving an equilibrium rate constant (k2) of 0.0187 g mg-1 min-1. The linear Langmuir isothermal model could more accurately describe the experimental data, indicating the adsorption process is mainly dominated by the complexation interactions between MTZE and Cu2+. The thermodynamic parameters of ΔG° (< 0), ΔH° (> 0), and ΔS° (> 0) further indicate that the adsorption is a spontaneous and endothermic, confirming that the complexation between Cu2+ and 3D GO-MTZE3:1 composite occurs. Due to its high selectivity for Cu2+, good hydrophobicity, and excellent stability, the developed 3D GO-MTZE3:1 composite possesses might be promisingly used in the aqueous selective enrichment/removal of Cu2+.

Adsorption of contaminants by nanomaterials synthesized by green and conventional routes: a critical review

Nanomaterials, due to their large surface area and selectivity, have stood out as an alternative for the adsorption of contaminants from water and effluents. Synthesized from green or traditional protocols, the main advantages and disadvantages of green nanomaterials are the elimination of the use of toxic chemicals and difficulty of reproducing the preparation of nanomaterials, respectively, while traditional nanomaterials have the main advantage of being able to prepare nanomaterials with well-defined morphological properties and the disadvantage of using potentially toxic chemicals. Thus, based on the particularities of green and conventional nanomaterials, this review aims to fill a gap in the literature on the comparison of the synthesis, morphology, and application of these nanomaterials in the adsorption of contaminants in water. Focusing on the adsorption of heavy metals, pesticides, pharmaceuticals, dyes, polyaromatic hydrocarbons, and phenol derivatives in water, for the first time, a review article explored and compared how chemical and morphological changes in nanoadsorbents synthesized by green and conventional protocols affect performance in the adsorption of contaminants in water. Despite advances in the area, there is still a lack of review articles on the topic.

Synergistic graphene-MnOx/honeycomb activated carbon (G-MnOx/HAC) and plasma technology for eradication of pathogenic microorganisms

This paper addresses the risk for environmental transmission of pathogenic microorganisms in confined spaces and the serious health hazards for personnel, and research on efficient eradication methods for the pathogenic microorganisms was carried out to provide technical support for ensuring the health of personnel in confined spaces. A series of graphene-MnO2 (G-MnO2) catalytic materials was prepared by hydrothermal and precipitation methods, and processing parameters such as the graphene doping method, the raw material ratio and the plasma action time were optimized. It was shown that G-MnOX-P/HAC prepared by a one-step precipitation method and with a graphene doping ratio of 10% had the best bactericidal effect in a dielectric barrier discharge (DBD) reactor after 4 min of reaction. The eradication rates for Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), coronavirus and Aspergillus niger were all greater than 99.9%. The characterization techniques TEM, SEM, XRD, XPS, BET and FT-IR showed that the G-MnOX-P samples prepared by the one-step precipitation method had larger specific surface areas with more oxygen vacancies and functional groups on the surfaces, which was conducive to decomposition of the ozone generated by the dissociated plasma and formation of reactive oxygen species (ROS) for the microbial eradication process. Finally, by comparing the ozone-decomposition activity with the plasma co-catalytic performance, it was verified that efficient decomposition of the ozone facilitated the eradication of microorganisms. Based on this, an analysis of the mechanism for efficient eradication was carried out.

Preparation of CaMgAl-calcined layered double hydroxides and application on the removal of phosphates

A calcined CaMgAl-layered double hydroxide nanocomposite, CaMgAl-LDH (CCMA-0.83-600), was prepared by introducing Mg on the basis of CaAl-LDHs for the removal of phosphate from wastewater. The structure of the as-synthesized CCMA-0.83-600 was confirmed by XRD and SEM analyses. Parameters affecting the adsorption process of phosphate adsorbed by CCMA-0.83-600 were thoroughly explored, such as initial pH, adsorbent dosage and co-existing anions. The adsorption kinetic study suggested that the adsorption process accorded with the pseudo-second-order kinetic model and the adsorption rate was controlled by both the liquid film diffusion and intra-particle diffusion. The adsorption isotherm study indicated the adsorption process followed by the Langmuir isotherm model. Thermodynamic analysis suggested that the adsorption of phosphate was spontaneous and exothermic. The obtained results indicated that CCMA-0.83-600 is a suitable candidate for the removal of phosphate from wastewater.

Bio-Fenton-Assisted Biological Process for Efficient Mineralization of Polycyclic Aromatic Hydrocarbons from the Environment

The intensive production of fossil fuels has led to serious polycyclic aromatic hydrocarbon (PAH) contamination in water and soil environments (as PAHs are typical types of emerging contaminants). Bio-Fenton, an alternative to Fenton oxidation, which generates hydrogen peroxide at a nearly neutral pH condition, could ideally work as a pretreatment to recalcitrant organics, which could be combined with the subsequent biological treatment without any need for pH adjustment. The present study investigated the performance of a Bio-Fenton-assisted biological process for mineralization of three typical types of PAHs. The hydrogen peroxide production, PAH removal, overall organic mineralization, and microbial community structure were comprehensively studied. The results showed that the combined process could achieve efficient chemical oxygen demand (COD) removal (88.1%) of mixed PAHs as compared to activated sludge (33.1%), where individual PAH removal efficiencies of 99.6%, 83.8%, and 91.3% were observed for naphthalene (NAP), anthracene (ANT), and pyrene (PYR), respectively, with the combined process.