Electron Beam Technology Coupled to Fenton Oxidation for Advanced Treatment of Dyeing Wastewater: from Laboratory to Full Application

This study developed a novel electron beam (EB) and Fenton process (FP) for the advanced treatment of dyeing wastewater by combining EB radiation with the FP. In the presence of 0.1 mM Fe­(II) and 0.1 mM H2O2, the mineralization efficiency of Rhodamine B was 59.21% at a dose of 2 kGy, which is higher than single EB radiation and the FP, due to the interaction of hydrated electron with Fe­(II) and H2O2, hydrated electron enhanced the activation of H2O2 and the conversion from Fe­(III) to Fe­(II) in the EB radiation process. For the actual dyeing wastewater with 255 mg/L COD and 150 times color, the COD decreased to 52 mg/L, and the color decreased to 10 times after EB & FP treatment. In addition, EB & FP was used as an advanced treatment process in practical application to treat the dyeing wastewater from a knitting factory and showed satisfactory performance. The treatment cost of EB & FP was estimated to be 1.5 ¥ per ton wastewater. In summary, EB & FP possesses strong oxidation capacity and low operational cost with the maximum treatment capacity of 5000 m3 per day per electron accelerator, which could provide a solution for the treatment of recalcitrant dyeing wastewater

Highly Efficient Photocatalytic H₂O₂ Production over a Zn_0.3Cd_0.7S/MXene Photocatalyst for Degradation of Emerging Pollutants under Visible-Light Irradiation

Hydrogen peroxide (H2O2) is an ideal green product with a broad range of applications, and visible-light-driven photocatalytic H2O2 production is deemed a sustainable and eco-friendly strategy. Herein, various ZnxCd1–xS/MXene photocatalysts with a Schottky junction were prepared for photocatalytic H2O2 production. The obtained Zn0.3Cd0.7S/MXene (ZCM-0.3) hybrid presented the highest photocatalytic H2O2 production rate in pure neutral water of 1160 μmol h–1 g–1, which was further improved to 2178.58 μmol h–1 g–1 in the presence of isopropanol as the sacrificial reagent. The experimental results demonstrated that the sufficient visible-light-harvesting ability and appropriate conduction band potential of the Zn0.3Cd0.7S solid solution, the excellent conductivity and two-electron selectivity of MXene, and the construction of Schottky junctions at the Zn0.3Cd0.7S/MXene interface resulted in the fast transfer and separation of the photogenerated charge carriers and the targeted reduction of oxygen to H2O2. The photocatalytic mechanism for H2O2 production was studied and proposed. Moreover, a simple photo-Fenton system consisting of ZnxCd1–xS/MXene and ferrous ions (Fe2+) was constructed and applied for the degradation of various emerging pollutants, which also performed effectively and exhibited universality across different pollutants. Overall, this study presents a novel and useful strategy to convert solar energy into chemical energy through efficient H2O2 production and provides an effective alternative for the degradation of emerging pollutants

Enhanced Photocatalytic Degradation of Emerging Contaminants Using Ti₃C₂T_<i>x</i> MXene-Supported CdS Quantum Dots

The synthesis of efficient and stable catalysts for photocatalytic reactions is still a challenge. In this study, a new photocatalyst composed of two-dimensional titanium carbide (Ti3C2Tx) and CdS quantum dots (QDs) was fabricated, in which CdS QDs were intimately anchored on the Ti3C2Tx sheet surface. Due to the specific interface characteristics of CdS QDs/Ti3C2Tx, Ti3C2Tx can considerably facilitate the generation of photogenerated charge carriers, their separation, and their transfer from CdS. As expected, the obtained CdS QDs/Ti3C2Tx exhibit outstanding photocatalytic performance for carbamazepine (CBZ) degradation. Moreover, the quenching experiments demonstrated that superoxide radicals (•O2–), H2O2, 1O2, and •OH are the reactive species involved in CBZ degradation, while •O2– made a major contribution. In addition, the sunlight-driven CdS QDs/Ti3C2Tx photocatalytic system is widely suitable for the elimination of different emerging pollutants in various water matrices, suggesting its potential practical environmental applications

Magnetic Nanoscaled Fe₃O₄/CeO₂ Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4‑Chlorophenol

Magnetic nanoscaled Fe₃O₄/CeO₂ composite was prepared by the impregnation method and characterized as a heterogeneous Fenton-like catalyst for 4-chlorophenol (4-CP) degradation. The catalytic activity was evaluated in view of the effects of various processes, pH value, catalyst addition, hydrogen peroxide (H₂O₂) concentration, and temperature, and the pseudo-first-order kinetic constant of 0.11 min^–1 was obtained for 4-CP degradation at 30 °C and pH 3.0 with 30 mM H₂O₂, 2.0 g L^–1 Fe₃O₄/CeO₂, and 0.78 mM 4-CP. The high utilization efficiency of H₂O₂, calculated as 79.2%, showed a promising application of the catalyst in the oxidative degradation of organic pollutants. The reusability of Fe₃O₄/CeO₂ composite was also investigated after six successive runs. On the basis of the results of metal leaching, the effects of radical scavengers, intermediates determination, and X-ray photoelectron spectroscopic (XPS) analysis, the dissolution of Fe₃O₄ facilitated by CeO₂ played a significant role, and 4-CP was decomposed mainly by the attack of hydroxyl radicals (•OH), including surface-bound •OH_ads generated by the reaction of Fe²⁺ and Ce³⁺ species with H₂O₂ on the catalyst surface, and •OH_free in the bulk solution mainly attributed to the leaching of Fe

Adsorption kinetics and isotherm models of heavy metals by various adsorbents: An overview

Heavy metal pollution has become one of the most severe environmental issues. Adsorption is an effective method for removing heavy metals from aquatic environments. The adsorption isotherm and kinetics models can provide information on the adsorption process, maximal adsorption capacity, and mass transfer steps, which are essential to evaluate the performance of an adsorbent and to design an adsorption system. In this review, the adsorption kinetics and isotherms of heavy metals by various adsorbents were summarized and discussed in depth. First, the sources of heavy metal pollution and the adsorption technology to remove heavy metals were reviewed. The adsorption capacity of Cu, Cd, Zn, Ni, Cr, As, Fe, Hg, Co, Sr, and Cs by biosorbents (e.g. algae, agriculture waste biochar/activated carbon, and bacteria) and by abiotic adsorbents (e.g. metal–organic frameworks (MOFs), microtubes, polymers, clays, minerals, and coal) were systematically summarized. Second, the origins, basic assumptions, importance, physical meanings, and applications of the adsorption kinetics and isotherm models were discussed in depth. Third, the methods for selecting adsorption models in different conditions were explained, and the statistical parameters which can be applied to evaluate the performance of the models were illustrated. Finally, two Excel sheets are provided for solving the adsorption models, which are available in Supplementary Information. This review article will deepen the understanding of the interaction between heavy metals and adsorbents and facilitate the development of adsorptive technology for heavy metal removal from water and wastewater.</p

Enhanced Sewage Sludge Disintegration and Hydrogen Production by Ionizing Radiation Pretreatment in the Presence of Fe²⁺

The effect of ferrous ion (Fe2+) on sludge disintegration by ionizing radiation and subsequent hydrogen production was studied. Sludge was pretreated with 20 kGy ionizing radiation at three pH levels (pH 3, 5, and 7) with 0–1000 mg/L Fe2+ dosages. Results showed that the sludge disruption was better promoted by Fe2+ at pH 5. The highest soluble chemical oxygen demand of 5.01 g/L (4.66 times that of control) was achieved with 800 mg/L Fe2+ addition at pH 5. Cumulative hydrogen production (CHP) was also enhanced in subsequent dark fermentation; a CHP of 26 mL H2/100 mL was 2 times and 1.73 times that of the control and sole radiation pretreated groups, respectively. Change of dissolved organics showed that ionizing radiation pretreatment mainly induced the release of protein-like organics, and the addition of Fe2+ further induced the solubilization of microbial byproduct-like organics. Sludge degradation was also promoted by Fe2+ addition. Microbial analysis showed that CHP had a significant positive correlation with Paraclostridium sp. and Clostridium tertium, and the addition of Fe2+ suppressed species that are negatively related to CHP. This study suggested that Fe2+ could significantly enhance the hydrogen production from sewage sludge by promoting sludge disintegration and affecting the microbial distribution

Magnetic Nanoscaled Fe₃O₄/CeO₂ Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4‑Chlorophenol

Magnetic nanoscaled Fe₃O₄/CeO₂ composite was prepared by the impregnation method and characterized as a heterogeneous Fenton-like catalyst for 4-chlorophenol (4-CP) degradation. The catalytic activity was evaluated in view of the effects of various processes, pH value, catalyst addition, hydrogen peroxide (H₂O₂) concentration, and temperature, and the pseudo-first-order kinetic constant of 0.11 min^–1 was obtained for 4-CP degradation at 30 °C and pH 3.0 with 30 mM H₂O₂, 2.0 g L^–1 Fe₃O₄/CeO₂, and 0.78 mM 4-CP. The high utilization efficiency of H₂O₂, calculated as 79.2%, showed a promising application of the catalyst in the oxidative degradation of organic pollutants. The reusability of Fe₃O₄/CeO₂ composite was also investigated after six successive runs. On the basis of the results of metal leaching, the effects of radical scavengers, intermediates determination, and X-ray photoelectron spectroscopic (XPS) analysis, the dissolution of Fe₃O₄ facilitated by CeO₂ played a significant role, and 4-CP was decomposed mainly by the attack of hydroxyl radicals (•OH), including surface-bound •OH_ads generated by the reaction of Fe²⁺ and Ce³⁺ species with H₂O₂ on the catalyst surface, and •OH_free in the bulk solution mainly attributed to the leaching of Fe

Metal Organic Framework with Coordinatively Unsaturated Sites as Efficient Fenton-like Catalyst for Enhanced Degradation of Sulfamethazine

A novel Fenton-like catalyst, metal organic framework MIL-100­(Fe) with FeII/FeIII mixed-valence coordinatively unsaturated iron center (CUS-MIL-100­(Fe)), was synthesized, characterized, and used for the degradation of sulfamethazine (SMT). The catalytic performance of CUS-MIL-100­(Fe) was investigated on the basis of various parameters, including initial pH, H2O2 concentration, catalyst dosage, and initial SMT concentration. The results showed that CUS-MIL-100­(Fe) could effectively degrade SMT, with almost 100% removal efficiency within 180 min (52.4% mineralization efficiency), under the reaction conditions of pH 4.0, 20 mg L–1 SMT, 6 mM H2O2, and 0.5 g L–1 catalyst. Moreover, CUS-MIL-100­(Fe) displayed a higher catalytic activity than that of MIL-100­(Fe) for SMT degradation. Combined with the physical–chemical characterization, the enhanced catalytic activity can be ascribed to the incorporation of FeII and FeIII CUSs (coordinatively unsaturated metal sites), the large specific surface area, as well as the formation of mesopores. Furthermore, CUS-MIL-100­(Fe) exhibited a good stability and reusability. The possible catalytic mechanism of CUS-MIL-100­(Fe) was tentatively proposed

Discrepant Catalytic Activity of Biochar-Based Fe and Co Homonuclear and Heteronuclear Diatomic Catalysts for Activating Peroxymonosulfate to Degrade Emerging Pollutants

In this study, biochar-based Fe and Co homonuclear (DAC–Fe–Co) and heteronuclear (DAC-Fe/Co) diatomic catalysts were first prepared via controlling the ligands of Fe and Co, and used to activate peroxymonosulfate (PMS) for the degradation of emerging organic pollutants, such as sulfamethoxazole (SMX), bisphenol A, phenol, atrazine, and nitrobenzene. The results showed that acid pretreatment of biochar was necessary for biochar to synthesize atomic catalysts. The DAC-Fe/Co had higher contents of Fe and Co than DAC–Fe–Co, but lower catalytic activity, in which the SMX first-order kinetics rate constant for DAC–Fe–Co was 4.1 times higher than that for DAC-Fe/Co, achieving 0.32 min–1. DAC–Fe–Co and DAC-Fe/Co could activate PMS to produce similar reactive species, including radicals and nonradicals. But DAC–Fe–Co produced a higher concentration of radicals than DAC-Fe/Co. The density functional theory (DFT) calculation indicated that compared to DAC-Fe/Co, DAC–Fe–Co had a higher adsorption capacity for PMS (−7.90 eV) and lower energy barrier for the regeneration of Fe (−1.20 eV) and Co (−1.16 eV) active sites. The enhanced regeneration of Fe and Co active sites promoted the formation of radicals, which explained the faster SMX removal rate in the system of DAC–Fe–Co/PMS than DAC-Fe/Co/PMS. The DAC–Fe–Co/PMS system exhibited high resistance to inorganic anions and showed excellent catalytic stability in the cycling experiments. This study provides insight into the discrepant catalytic activity of homonuclear and heteronuclear diatomic catalysts for PMS activation to degrade emerging organic contaminants, and offers a new way to prepare the homonuclear diatomic catalyst

Aptamer-Based Au Nanoparticles-Enhanced Surface Plasmon Resonance Detection of Small Molecules

Small molecules are difficult to detect by conventional SPR technique directly because the changes in the refractive index resulting from the binding processes of small biomolecules are often small. In order to extend the application of SPR biosensor in detecting a small molecule, we combine the advantage of aptamer technique with the amplifying effect of Au nanoparticles to design a sensitive SPR sensor for detecting small molecules. The principle of this sensor is based on surface inhibition detection. The aptamer is first immobilized on SPR gold film with its ss-DNA structure. The aptamer possessing this structure can be hybridized with Au nanoparticles-tagged complementary ss-DNA and result in a large change of SPR signal. However, the aptamer will change its structure from ss-DNA to tertiary structure after adenosine is added to the SPR cell. The aptamer possessing tertiary structure could not hybridize with Au nanoparticles-tagged complementary ss-DNA. Thus, the change of SPR signal resulted in the hybridization reaction between aptamer and Au nanoparticles-tagged complementary ss-DNA will decrease with the increase of the number of aptamers possessing tertiary structure, which is proportional to the concentration of the small molecule. Based on this principle, we choose a simple system (antiadenosine aptamer/adenosine) to detect the sensing ability of this SPR biosensor for a small molecule. The experimental results confirm that the SPR sensor we developed possesses a good sensitivity and a high selectivity for adenosine. The detection range for adenosine is from 1 × 10−9 to 1 × 10−6 M. More significantly, it is fairly easy to generalize this strategy to detect a spectrum of small molecules by SPR spectroscopy using different aptamers. Therefore, it is expected that this method may offer a new direction in designing high-performance SPR biosensors for sensitive and selective detection of a wide spectrum of small molecules