Rice hull/MnFe2O4 composite: preparation, characterization and its rapid microwave-assisted COD removal for organic wastewater

Recent progress, trends, and new challenges in the electrochemical production of green hydrogen coupled to selective electrooxidation of 5-hydroxymethylfurfural (HMF)

The production of clean electrical energy and the correct use of waste materials are two topics that currently concern humanity. In order to face both problems, extensive work has been done on the electrolytic production of green H2 coupled with the electrooxidative upgrading of biomass platform molecules. 5-Hydroxymethylfurfural (HMF) is obtained from forest waste biomass and can be selectively oxidized to 2,5-furandicarboxylic acid (FDCA) by electrochemical pathways. FDCA is an attractive precursor to polyethylene furanoate (PEF), with the potential to replace petroleum-based polyethylene terephthalate (PET). An integrated electrochemical system can simultaneously produce H2 and FDCA at a lower energy cost than that required for electrolytic water splitting. Here, the benefits of the electrochemical production of H2 and FDCA over other production methods are presented, as well as the innovative applications of each reaction product and the advantages of carrying out both reactions in a coupled system. The recently reported progress is disclosed, through an exploration of electrocatalyst materials used in simultaneous production, including the use of nickel foams (NF) as modification substrates, noble and non-noble metals, metal non-oxides, metal oxides, spinel oxides and the introduction of oxygen vacancies. Based on the latest trends, the next challenges associated with its large-scale production are proposed for its implementation in the industrial world. This work can offer a guideline for the detailed understanding of the electrooxidation of HMF towards FDCA with the production of H2, as well as the design of advanced electrocatalysts for the sustainable use of renewable resources.

Preparation of 3D network CNTs-modified nickel foam with enhanced microwave absorptivity and application potential in wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) modified nickel foams (MWCNTs-NF) were developed with an electrophoretic deposition methodology for microwave (MW) assisted catalysis and processing enhancement. A nickel foam (NF) was selected to serve the dual purpose both as the MW absorbing catalytic materials and the matrix for MWCNTs loading in order to maximize the recyclability of the catalysts. The effects of electrophoretic voltage and concentration of electrophoretic fluid on the morphology and deposition characteristics of MWCNTs on the NF matrix were investigated. It was found that the MWCNTs-NF composite material resulted in strong enhancement of MW absorptivity with synergistic heat-generating effects that were not observed when MWCNTs or NF was exposed to MW alone. The combination of NF and MWCNTs brought a catalytic total organic carbon removal efficiency of 97% in wastewater treatment, while that using bare MWCNTs and NF were only 65.2% and 79.3%, respectively. The coupling of NF with MWCNTs led to the formation of additional MW-absorbing channels and focal sites with strong MW absorptivity, which in turn gave rise to the synergistic MW heating effects. This research highlights the great prospect of the MW-assisted reaction enhancement using the MWCNTs-NF composite material as the catalyst in wastewater treatment and other similar engineering applications.

Synthesis and high-resolution structural and chemical analysis of iron-manganese-oxide core-shell nanocubes

We have investigated the structure and chemical composition of nanoparticles synthesized by thermal decomposition of a mixture of iron oleate and manganese oleate in a high-boiling solvent in the presence of Na-oleate and oleic acid as surfactants by analytical transmission electron microscopy (TEM). The particles appear core-shell like in bright field TEM images. Higher spatial resolution TEM (HRTEM) analysis reveals a FeO/MnO like structure in the core and a spinel like structure in the shell. With high-resolution analytical methods like energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), the distribution of the metals Mn and Fe was investigated. Differences in the oxidation state of these metals were found between the core and the shell region. The presence of sodium from the used surfactant (Na-oleate) on the surface of the particles has been proved.

A comprehensive review of applications of magnetic graphene oxide based nanocomposites for sustainable water purification

With the rapid growth of industrialization, water bodies are polluted with heavy metals and toxic pollutants. In pursuit of removal of toxic pollutants from the aqueous environment, researchers have been developed many techniques. Among these techniques, magnetic separation has caught research attention, as this approach has shown excellent performance in the removal of toxic pollutants from aqueous solutions. However, magnetic graphene oxide based nanocomposites (MGO) possess unique physicochemical properties including excellent magnetic characteristics, high specific surface area, surface active sites, high chemical stability, tunable shape and size, and the ease with which they can be modified or functionalized. As results of their multi-functional properties, affordability, and magnetic separation capability, MGO's have been widely used in the removal of heavy metals, radionuclides and organic dyes from the aqueous environment, and are currently attracting much attention. This paper provides insights into preparation strategies and approaches of MGO's utilization for the removal of pollutants for sustainable water purification. It also reviews the preparation of magnetic graphene oxide nanocomposites and primary characterization instruments required for the evaluation of structural, chemical and physical functionalities of synthesized magnetic graphene oxide nanocomposites. Finally, we summarized some research challenges to accelerate the synthesized MGO's as adsorbents for the treatment of water pollutants such as toxic and radioactive metal ions and organic and agricultural pollutants.

Preparation of hollow iron/halloysite nanocomposites with enhanced electromagnetic performances

Nanostructures loaded on halloysite nanotubes (HNTs) have attracted global interest, because the nanotubular HNTs could extend the range of their potential applications. In this study, we fabricated a novel nanocomposite with hollow iron nanoparticles loaded on the surface of HNTs. The structure of the iron nanoparticles can be adjusted by ageing time. Owing to the increased remnant magnetization and coercivity values, the nanocomposites loaded with hollow iron nanoparticles showed better electromagnetic performance than that with solid iron nanoparticles. This study opens a new pathway to fabricate halloysite nanotubular nanocomposites that may gain applications in the catalytic degradation of organic pollutants and electromagnetic wave absorption.

Mn3O4/graphene nanocomposites: outstanding performances as highly efficient photocatalysts and microwave absorbers

Mn₃O₄ incorporated graphenes synthesized by a deposition-solvothermal process were efficiently used for methylene blue degradation under visible illumination (88 W, λ > 420 nm) and under microwave irradiation (800 W, 2.45 GHz, 373 K).

Preparation of activated carbon from edible fungi residue by microwave assisted K2CO3 activation--application in reactive black 5 adsorption from aqueous solution

Preparation of activated carbon from the edible fungi residue (EFR) by microwave assisted K(2)CO(3) activation was studied. The optimum preparation conditions were as follows: radiation time of 16 min, K(2)CO(3)/EFR ratio of 0.8 and microwave power of 520 W. The iodine number, the amount of methylene blue adsorption and the yield of activated carbon prepared under optimum conditions were 732.74, 172.43 mg/g and 23.0%, respectively. The activated carbon was characterized by SEM, FT-IR, N(2) adsorption and pH(ZPC), and then they were used as adsorbent for removing reactive black 5 from aqueous solution. The highest removal efficiency of 100% could be achieved at the solution pH of 2.0, the adsorption efficiency descended with the increasing of pH and the optimum activated carbon dose was 8.75 g/L. The Langmuir isotherm well fit the adsorption process with the complete monolayer adsorption capacity of 19.6 mg/g and the equilibrium adsorption constant of 0.39 L/mg.

Carbofuran degradation by the application of MW-assisted H₂O₂ process

Carbofuran removal performance of a microwave (MW)-assisted H₂O₂ system under different MW-power levels (300-900 W) was investigated. Batch experiments were conducted at 100 mg/L carbofuran concentration using a modified-MW reactor with 2450 MHz of fixed frequency. As a precursor, control experiments were carried out with H₂O₂ alone, MW alone and conventional heating (CH). A maximum carbofuran removal of 14 % was observed in both H₂O₂ alone and CH systems. On the other hand, only 2 % removal was observed in the MW alone system irrespective of the operation-mode, i.e. continuous or pulsed. The combination of MW and H₂O₂ produced 100 % carbofuran removal in all the MW-assisted experiments. The MW-assisted system operated under continuous-mode and at 750 W has showed rapid carbofuran degradation, i.e. 30 sec, with the highest first-order removal rate constant of 25.82/min. However, 97 % carbon oxygen demand (COD) removal was observed in the same system only after 30 min. On the other hand, 100 % carbofuran removal and 49 % COD removal were observed in the pulsed-mode MW-assisted H₂O₂ system after 10 and 30 min, respectively. Carbofuran mineralization in the system was evidenced by the formation of ammonium and nitrate, and carbofuran intermediates.

Fabrication of nanospinel ZnCr2O4 using sol-gel method and its application on removal of azo dye from aqueous solution

For the first time, nanoparticles of zinc chromite, spinel ZnCr(2)O(4) have been fabricated by the thermal decomposition of Zn-Cr gel prepared by sol-gel method in the presence of oxalic acid as a chelating agent. It was shown that the well-crystallized spinel structure is formed after calcination at 450°C. The nanospinel has been characterized by differential thermal analysis (DTA), X-ray powder diffraction (XRD), infrared spectroscopy (IR), and transmission electron microscope (TEM). The average particle size is approximately 13 nm according to the TEM image. The nanoparticles of zinc chromites showed excellent adsorption properties towards reactive dye, reactive blue 5 (RB5). The adsorption studies have been carried out for contact time, different pH values, different temperatures, and adsorbent doses. The investigation of removal kinetics of RB5 indicates that the removal process obeys the rate of second-order kinetic equation. The results indicate that the Langmuir adsorption isotherm fitted the data better than the Freundlich. Also, the photocatalytic degradation of RB5 using spinel ZnCr(2)O(4) under UV irradiation at pH=1 has been also examined. The results showed that the degradation of RB5 dye follows merely an adsorption process.