One-step preparation of a novel graphitic biochar/Cu0/Fe3O4 composite using CO2-ambiance pyrolysis to activate peroxydisulfate for dye degradation

Silicone-modified black peanut shell (BPS) biochar adsorbents: Preparation and their adsorptions for copper(II) from water

Novel silicone-modified biochar adsorbents (BPS-MBCs) were prepared by utilizing waste black peanut shell (BPS) as a raw biochar and gamma-amino-propyl triethoxysilane (silicone) as an inorganic modifier. The novelty of this work is that the incorporation of silicone into BPS can rise the specific surface area and porosity of BPS-MBCs and elevate their adsorptions for copper (II). Sorption kinetics data for copper (II) were molded using five kinetic equations [i.e. Lagergren 1st-order and 2nd-order, intraparticle diffusion (IN-D), Elovich, and Diffusion-chemisorption]. The equilibrium adsorption data for copper (II) were analyzed using two-parameter isotherm equations [i.e. Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin] and three-parameter Sips, Redlich-Peterson and Toth isotherm models. It was validated that copper (II) sorption on BPS-MBCs matched better with pseudo-2nd-order kinetic, Diffusion-chemisorption and Langmuir isotherm models. The maximal qmLan of BPS-MBC-400 was near 284 mg/g at 45 °C. By multi-phase fitting of IN-D modelling, intra-particle diffusion coefficient (kin-d) and diffusion coefficient of external mass-transfer (DEx-Di) for copper (II) were calculated. The low sorption energy from Temkin and mean free energy from D-R modellings implied that copper (II) sorption was initiated by weak non-covalent bond interactions. Thermodynamic parameters indicated that copper (II) on BPS-MBCs was an endothermic and spontaneous process. Recycling of BPS-MBC-400 for copper (II) suggested it has excellent reusability. The major mechanism of copper (II) on BPS-MBCs is possibly comprised of multiple processes, such as physical adsorption (electrostatic attraction), chemical adsorption (adsorption from functional groups, chelation, and ion exchange) and diffusion-chemisorption. Based on these findings, it is expects that BPS-MBCs are promising sorbents for copper (II) eradication from Cu(II)-including wastewater.

Non-radical activation of persulfate with Bi2O3/BiO1.3I0.4 for efficient degradation of propranolol under visible light

Non-radical activation of persulfate (PS) by photocatalysts is an effective approach for removing organic pollutants from aqueous environments. In this study, a novel Bi2O3/BiO1.3I0.4 heterojunction was synthesized using a facile solvothermal approach and used for the first time for non-radical activation of PS to degrade propranolol (PRO) in the presence of visible light. The findings found that the degradation rate of PRO in the Bi2O3/BiO1.3I0.4/PS system was significantly increased from 19% to more than 90% within 90 min compared to the Bi2O3/BiO1.3I0.4 system. This indicated that the composite system exerted an excellent synergistic effect between the photocatalyst and the persulfate-based oxygenation. Quenching tests and electron paramagnetic resonance demonstrated that the non-radical pathway with singlet oxygen as the active species played a major role in the photocatalytic process. The existence of photo-generated holes during the reaction could also be directly involved in the oxidation of pollutants. Meanwhile, a possible PRO degradation pathway was also proposed. Furthermore, the impacts of pH, humic acid and common anions on the PRO degradation by the Bi2O3/BiO1.3I0.4/PS were explored, and the system's stability and reusability were also studied. This study exhibits a highly productive catalyst for PS activation via a non-radical pathway and provides a new idea for the degradation of PRO.

Progress of metal-loaded biochar-activated persulfate for degradation of emerging organic contaminants

In recent years, studies on the degradation of emerging organic contaminants by sulfate radical (SO4-·) based advanced oxidation processes (SR-AOPs) have triggered increasing attention. Metal-loaded biochar (Me-BC) can effectively prevent the agglomeration and leaching of transition metals, and its good physicochemical properties and abundant active sites induce outstanding in activating persulfate (PS) for pollutant degradation, which is of great significance in the field of advanced oxidation. In this paper, we reviewed the preparation method and stability of Me-BC, the effect of metal loading on the physicochemical properties of biochar, the pathways of pollutant degradation by Me-BC-activated PS (including free radical pathways: SO4-·, hydroxyl radical (·OH), superoxide radicals (O2-·); non-free radical pathways: singlet oxygen (1O2), direct electron transfer), and discussed the activation of different active sites (including metal ions, persistent free radicals, oxygen-containing functional groups, defective structures, etc.) in the SR-AOPs system. Finally, the prospect was presented for the current research progress of Me-BC in SR-AOPs technology.

Metal Oxide-Impregnated Biochar for Azo Dye Remediation as Revealed through Kinetics, Thermodynamics, and Response Surface Methodology

This study reports for the first time the adsorption capacity of a novel adsorbent Croton bonplandianus Baill. biochar. Its adsorption capacity was further enhanced by loading magnetic composites on it, which makes it an efficient medium for the adsorption of dyes. Two azo dyes, Basic Brown 1 (BB1) and Basic Orange 2 (BO2), were studied for their effective adsorption from aqueous media. A comprehensive characterization was performed by using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) to study the properties of Fe2O3-loaded C. bonplandianus Baill. biochar (FO-CBPBB). A series of batch experiments were conducted to optimize various parameters (pH, contact time, adsorbent amount, initial BB1 and BO2 concentrations, and temperature) for the maximum adsorption of BB1 and BO2 on the FO-CBPBB adsorbent. The percentage of BB1 and BO2 dyes that adsorb to FO-CBPBB under the best experimental circumstances (pH of solution 7, contact time 80 min, temperature of solution 40 °C, initial BB1 and BO2 dye concentrations 80 mg L-1, and adsorbent dose 1 g L-1) was 93 and 95%, respectively. The best adsorption of BB1 and BO2 was accomplished by optimizing the effects of several factors, including the starting dye concentration, contact time, and temperature, based on the central composite design. The Freundlich and Langmuir isotherm models were used to examine the equilibrium data. The Langmuir isotherm with the greatest adsorption capacity and R2 value effectively captured the experimental results. When kinetic parameters were investigated, it was found that pseudo-second-order was appropriate, reflecting the fact that the dye-adsorbent interaction was the rate-controlling factor in this study. The sorption process was endothermic and spontaneous, as shown by the thermodynamic variables. Based on the interaction between the adsorbent and azo dyes, it was concluded that the adsorption process was electrostatic in nature. Adsorbents that have been synthesized can effectively remove azo dyes from wastewater. Excellent regeneration efficiency was exhibited by FO-CBPBB, which makes it an eco-friendly and cost-effective alternative to other costly techniques applied for water purification.

Production of C5-C12 olefins by catalytic pyrolysis of low-density polyethylene with MCM-41 in CO2/N2

The current high volume of plastic waste, but low recycling rate, has led to environmental pollution and wasted energy. Greenhouse gas CO2 can facilitate thermal cracking to dehydrogenate waste plastics, and has potential value for producing olefins. In this work, the pyrolysis properties of low-density polyethylene (LDPE) were studied by thermogravimetric analysis and Py-GC/MS. The effect of the pyrolysis atmosphere, using N2 or CO2, with various MCM-41 catalyst ratios on pyrolysis product distribution, were investigated. The experimental results show that the olefin selectivity under a N2 atmosphere was from 30.32 % to 44.66 % which increased as the MCM-41 catalyst was increased. Under a CO2 atmosphere, the olefin selectivity reached a maximum of 60.39 %. The Boudouard reaction was also enhanced by the introduction of CO2. The carbon content of the subdivided olefins showed that in CO2, the promotion of C5-C12 olefins was relatively weak when non-catalyzed or at low catalytic ratios, but increased significantly at higher MCM-41 catalyst ratios. With a ratio of LDPE: MCM-41 = 5:4, the CO2 atmosphere showed the greatest promotion of C5-C12 olefins over N2, with an increase of 14.66 % compared to N2, representing a 48.54 % yield of the liquid product. Producing C5-C12 olefins under these conditions maximized energy efficiency. These results show that catalytic pyrolysis of LDPE under a CO2 atmosphere has great potential to produce C5-C12 olefins, which can be used to produce high-value chemicals such as naphtha and gasoline. This opens new opportunities for the chemical recycling of plastic waste.

UV-activated persulfates oxidation of anthraquinone dye: Kinetics and ecotoxicological assessment

Sulfate radical-based advanced oxidation processes (SR-AOPs) are gaining popularity as a feasible alternative for removing recalcitrant pollutants in an aqueous environment. Persulfates, namely peroxydisulfate (PDS) and peroxymonosulfate (PMS) are the most common sulfate radical donors. Persulfates activation by ultraviolet (UV) irradiation is considered feasible due to the high concentration of radicals produced as well as the lack of catalysts leaching. The research focuses on determining the impact of activated PDS and PMS on the degradation of anthraquinone dye, i.e., Acid Blue 129 (AB129). UV-activated PDS and PMS can quickly degrade the AB129 as well as restrict the formation of by-products. This could explain the reduced ecotoxicity levels of the treated water after degradation, using an aquatic plant (Lemna minor) and a crustacean (Daphnia magna). This, on the other hand, can ensure that the sulfate radical-based processes can be an environmentally friendly technology.

Simultaneously Cationic and Anionic Dyes Elimination via Magnetic Hydrochar Prepared from Copper Slag and Pinewood Sawdust

In practical wastewater, cationic and anionic dyes usually coexist, while synergistic removal of these pollutants is difficult due to their relatively opposite properties. In this work, copper slag (CS) modified hydrochar (CSHC) was designed as functional material by the one-pot method. Based on characterizations, the Fe species in CS can be converted to zero-valent iron and loaded onto a hydrochar substrate. The CSHC exhibited efficient removal rates for both cationic dyes (methylene blue, MB) and anionic dyes (methyl orange, MO), with a maximum capacity of 278.21 and 357.02 mg·g^-1, respectively, which was significantly higher than that of unmodified ones. The surface interactions of MB and MO between CSHC were mimicked by the Langmuir model and the pseudo-second-order model. In addition, the magnetic properties of CSHC were also observed, and the good magnetic properties enabled the adsorbent to be quickly separated from the solution with the help of magnets. The adsorption mechanisms include pore filling, complexation, precipitation, and electrostatic attraction. Moreover, the recycling experiments demonstrated the potential regenerative performance of CSHC. All these results shed light on the co-removal of cationic and anionic contaminates via these industrial by-products derived from environmental remediation materials.

Co-immobilized bienzyme of horseradish peroxidase and glucose oxidase on dopamine-modified cellulose-chitosan composite beads as a high-efficiency biocatalyst for degradation of acridine

Co-immobilized bienzyme biocatalysts are attracting increasing interest in the field of wastewater treatment due to their widespread application. In this study, we successfully prepared a co-immobilized bienzyme biocatalyst by immobilizing horseradish peroxidase (HRP) and glucose oxidase (GOD) on dopamine (DA) modified cellulose (Ce)-chitosan (Cs) composite beads via covalent binding, designated as Ce-Cs@DA/HRP-GOD beads, and found that the bienzyme biocatalyst had a good ability to catalytically degrade acridine in wastewater. SEM, EPR, FTIR, and XRD were used to characterise the structure and properties of the Ce-Cs@DA/HRP-GOD beads. The co-immobilized bienzyme biocatalyst with a small amount of HRP exhibited better degradation efficiency for acridine (99.5%, 8 h) in simulated wastewater compared to the Ce-Cs@DA/HRP (93.8%, 8 h) and Ce-Cs@DA/GOD (15.8%, 8 h) beads alone. In addition, a reusability study showed that the co-immobilized bienzyme biocatalyst maintained a degradation rate of 61.2% after six cycles of acridine degradation. The good biodegradability and reusability of the biocatalyst might be due to the synergistic effect of bienzyme HRP-GOD, including the strong covalent bonding. Accordingly, the co-immobilized bienzyme biocatalyst based on the cascade reaction may pave the way for efficient and eco-friendly treatment of industrial wastewater.