Novel RGO/α-FeOOH supported catalyst for Fenton oxidation of phenol at a wide pH range using solar-light-driven irradiation

Fenton-like system of UV/Glucose-oxidase@Kaolin coupled with organic green rust: UV-enhanced enzyme activity and the mechanism of UV synergistic degradation of photosensitive pollutants

This study introduces the UV/glucose-oxidase@Kaolin (GOD@Kaolin) coupled organic green rust (OGR) system (UV/OGR/GOD@Kaolin) to investigate the promotion of glucose oxidase activity by UV light and its synergistic degradation mechanism for photosensitive pollutants, specifically targeting the efficient degradation of 4-chlorophenol (4-CP). The enzyme system demonstrates its ability to overcome drawbacks associated with traditional Fenton systems, including a narrow pH range and high localized concentration of H2O2, by gradually releasing hydrogen peroxide in situ within a neutral environment. In the presence of UV radiation under specific conditions, enhanced enzyme activity is observed, resulting in increased efficiency in pollutant removal. The gradual release of hydrogen peroxide plays a crucial role in preventing unwanted reactions among active substances. These unique features facilitate the generation of highly reactive species, such as Fe(IV)O, •OH, and •O2-, tailored to efficiently target the organic components of interest. Additionally, the system establishes a positive iron cycle, ensuring a sustained reactive capability throughout the degradation process. The results highlight the UV/OGR/GOD@Kaolin system as an effective and environmentally friendly approach for the degradation of 4-CP, and the resilience of the enzyme extends the system's applicability to a broader range of scenarios.

Photocatalytic degradation of fluoranthene in soil suspension by TiO2/α-FeOOH with enhanced charge transfer capacity

Polycyclic aromatic hydrocarbons (PAHs) in soil are potentially harmful to human health. However, the use of photocatalysis technology to treat soil contaminated with PAHs remains challenging. Therefore, TiO2/α-FeOOH composite photocatalyst has been synthesized by hydrothermal method and sol-gel method and applied to photocatalytic degradation of fluoranthene in soil. The morphology, elements, crystal structure, optical properties, electrochemical characteristics, and photocatalytic activity of TiO2/α-FeOOH have been characterized. Results showed that TiO2 is tightly fixed on the surface of α-FeOOH, and TiO2/α-FeOOH had higher photocatalytic activity on photocatalytic degradation of fluoranthene in soil under simulated sunlight. The degradation efficiency of TiO2/α-FeOOH is 3.0 and 4.8 times higher than that of TiO2 and α-FeOOH, respectively. This is attributed to enhanced photocatalytic ability by enhancing the transfer capacity of electrons and holes and broadening the spectrum absorption range. The highest degradation efficiency was achieved when the pH of the soil is neutral, the ratio of water/soil is 10:1, and the dosage of catalyst is 50 mg/g. In addition, it was proved that •O2-, h+, and 1O2 are the main active substances in the photocatalysis of TiO2/α-FeOOH. The possible mechanism of a Z-type electron transfer structure was also proposed. The degradation products of fluoranthene were detected, and the degradation pathway was deduced.

Iron-bearing mining reject as an alternative and effective catalyst for photo-Fenton oxidation of phenol in water

In this work, iron-bearing mining reject was employed as an alternative and potential low-cost catalyst to degrade phenol in water by photo-Fenton strategy. Various techniques, including SEM-EDS, BET, FTIR, and XRD, were applied to evaluate the material's properties. Process parameters such as hydrogen peroxide concentration, catalyst dosage, and pH were studied to determine the optimum reaction conditions ([catalyst] = 0.75 g L-1, [H2O2] = 7.5 mM, and pH = 3). Phenol degradation and mineralization efficiencies at 180 and 300 min were 96.5 and 78%, respectively. These satisfactory results can be associated with the iron amount present in the waste sample. Furthermore, the material showed high catalytic activity and negligible iron leaching even after the fourth reuse cycle. The degradation behavior of phenol in water was well represented by a kinetic model based on the Fermi function. The iron-bearing mining reject can be considered a potential photo-Fenton catalyst for phenol degradation in wastewater.

Graphene-based photocatalysts for degradation of organic pollution

Compared with the traditional wastewater treatment technology, semiconductor photocatalysis is a rapidly emerging environment-friendly and efficient Advanced Oxidation Process for degradation of refractory organic contaminants. Single-component semiconductor photocatalysts exhibit poor photocatalytic performance and cannot meet the requirements of wastewater treatment. The combination of semiconductor photocatalysts and Graphene can effectively improve the photocatalytic activity and stability of semiconductor photocatalysts. This review focuses on the synergistic effect of several types of semiconductors with Graphene for photocatalytic degradation of organic pollutants. After a brief introduction of the photodegradation mechanism of semiconductor materials and the basic description of Graphene, the synthesis, characterization and degradation performance of various Graphene-based semiconductor photocatalysts are emphatically introduced.

Bisthiourea immobilized UiO-66-NH2 supported Fe2O3 nanoparticles to accelerate dual centers Fenton-like reaction

In this paper, an efficient catalyst UiO-66-BTU/Fe₂O₃ was synthesized by using bisthiourea modified zirconium-based metal organic framework (Zr-MOF). The UiO-66-BTU/Fe₂O₃ system features outstanding Fenton-like activity that is 22.84 times and 12.91 times larger than Fe₂O₃ and conventional UiO-66-NH₂/Fe₂O₃ system. It also exhibits good stability, broad pH range and recycle ability. Through comprehensive mechanistic investigations, we have ascribed the excellent catalytic performance of the UiO-66-BTU/Fe₂O₃ system to ¹O₂ and HO as the reactive intermediates, cause Zr centers can make complexation with Fe to form dual centers. Meanwhile, the CS on the bisthiourea can form Fe-S-C bonds with Fe₂O₃, reducing the redox potential of Fe(III)/Fe(II) and influencing the decomposing of H₂O₂, which indirectly regulate the interaction between Fe and Zr to accelerate electron transfer during the reaction. This work exhibits the design and understanding of the iron oxides incorporated in modified MOFs with excellent Fenton-like catalytic performance to remove phenoxy acid herbicides.

Reduced Graphene Oxide-Coated CuFeO2 with Fenton-like Catalytic Degradation Performance for Terramycin

A novel Fenton-like catalyst made of reduced graphene oxide-coated CuFeO₂ (rGO-coated CuFeO₂) was synthesized by the hydrothermal reaction method to remove terramycin from aqueous solutions. The catalytic degradation performance of rGO-coated CuFeO₂ for terramycin was verified with H₂O₂ activation. The characterization reveals that rGO-coated CuFeO₂ has a micro- and mesoporous structure, with groups such as C=C/C-C, CH₂-CO, and HO-C=O found on the surface. The Fenton-like catalytic degradation of terramycin by rGO-coated CuFeO₂ was in line with the pseudo-second-order kinetic model, and the elevated temperature accelerated the reaction. Terramycin was catalytically degraded by rGO-coated CuFeO₂ in two steps: terramycin was first adsorbed by rGO, and then Fenton-like degradation took place on its surface. This research presents new insight into the design and fabrication of Fenton-like catalysts with enhanced performance.

Magnetic TiO2/Fe3O4-Chitosan Beads: A Highly Efficient and Reusable Catalyst for Photo-Electro-Fenton Process

Heterogeneous photo-electro-Fenton process is an attractive technology for the removal of recalcitrant pollutants. To better exploit the presence of an irradiation source, a bifunctional catalyst with TiO2 nanoparticles embedded into an iron–chitosan matrix was developed. The catalytic activity of the catalyst was improved by the optimization of the loaded TiO2content. The prepared composite catalysts based on TiO2, Fe3O4 and chitosan were called TiO2/Fe3O4-CS beads. The best catalyst with an optimal ratio TiO2/Fe = 2 exhibited a high efficiency inthe degradation and mineralization of chlordimeform (CDM) insecticide. Under the optimum conditions (concentration of catalyst equal to 1 g L−1 and applied current intensity equal to 70 mA), a real effluent doped with 30 mg L−1 of CDM was efficiently treated, leading to 80.8 ± 1.9% TOC reduction after 6 h of treatment, with total removal of CDM after only 1 h.The generated carboxylic acids and minerals wereidentified and quantified. Furthermore, the stability and reusability of the developed catalyst was examined, and an insignificant reduction in catalytic activity was noticed forfour consecutive cycles of the photo-electro-Fenton process. Analyses using SEM, XRD and VSM showed a good stability of the physicochemical properties of the catalyst after use.

α-(Fe, Cu)OOH/RGO nanocomposites for heterogeneous photo-Fenton-like degradation of ciprofloxacin under visible light irradiation

Ciprofloxacin (CIP) is a third-generation fluoroquinolones (FQs) antibiotic, and the occurrence of CIP in the water environment has raised growing concerns owning to its environmental toxicity. In this paper, a novel α-(Fe, Cu)OOH/RGO nanocomposite was synthesized via a one-step reflux method for CIP degradation through a photo-Fenton-like process. When the RGO content was 1 wt%, CIP degradation ratio by the α-(Fe, Cu)OOH/RGO nanocomposite reached 100% under visible light irradiation within 120 min, and total organic carbon (TOC) removal ratio reached 60% within 180 min. The result of molecular fluorescence spectra highlighted that the loading of RGO on the α-(Fe, Cu)OOH significantly increased the content of hydroxyl radicals (·OH) in the heterogeneous photo-Fenton-like system and simultaneously inhibited the recombination of photogenerated electron and hole, which played critical roles in the enhancement of CIP degradation. In addition, 11 main intermediates were identified as the degradation products of CIP in the α-(Fe, Cu)OOH/RGO/H₂O₂/visible light reaction systems using liquid chromatograph-mass spectrometer (LC-MS) analyses. The results demonstrated that three degradation pathways for CIP removal by α-(Fe, Cu)OOH/RGO nanocomposite occurred, including (i) oxidation on the piperazine ring and dealkylation, (ii) defluorination and decarboxylation, and (iii) hydroxylation on the quinolone ring. This work would provide a novel insight of CIP degradation pathways in photo-Fenton-like processes.

Graphene oxide mediated Fe(III) reduction for enhancing Fe(III)/H2O2 Fenton and photo-Fenton oxidation toward chloramphenicol degradation

Slow reduction of Fe(III) in iron-mediated Fenton-like systems strongly limits the decomposition of H₂O₂ to produce hydroxyl radicals (^•OH). Here, we report that graphene oxide (GO) possesses excellent reactivity to enhance the Fe(III)/H₂O₂ Fenton and photo-Fenton oxidation for degrading chloramphenicol (CAP). EPR analysis and quenching tests reveal that ^•OH is the primary oxidant for CAP degradation. The characterization analysis and iron species transformation experiments demonstrate that Fe(III) can combine with the functional groups on the GO surface to form GO-Fe(III) complexes. The chronopotentiometry and cyclic voltammogram suggest that GO can donate electrons to Fe(III) via intramolecular electron transfer and promote H₂O₂ induced Fe(III) reduction by increasing the oxidation capability of Fe(III) due to the formation of GO-Fe(III) complexes, resulting in the strong promotion of the Fe(III)/Fe(II) cycle for producing OH. Moreover, the dark- and vis-GO/Fe(III)/H₂O₂ systems can effectively degrade CAP at initial pH ranging from 2.0 to 4.7. The reusability and stability of GO were evaluated by performing the cyclic degradation experiments of CAP. The OH induced degradation pathway of CAP was proposed involving three stages, based on intermediates analysis of UPLC-QTOF-MS/MS system. Therefore, the GO/Fe(III)/H₂O₂ system with or without visible light shows high potential for application in environmental remediation.

Bimetallic Cu/Fe Catalysts for Ibuprofen Mineralization

At present, the use of conventional wastewater processes is becoming increasingly challenging, mainly due to the presence of biorecalcitrant organic matter. Advanced oxidation processes such as Fenton, Fenton-like and hybrid processes have been successfully employed for the treatment of highly concentrated and toxic non-biodegradable pollutants. Here, a series of bimetallic catalysts, based on Cu/Fe supported over ZrO2, were investigated for the mineralization of ibuprofen with a heterogeneous Fenton-like reaction. The materials were prepared by incipient wetness impregnation and characterized by standard techniques. Temperature-programmed experiments highlighted the promotion of the reduction in CuO due to the synergistic effects of the coupled redox cycles of copper (Cu2+/Cu+) and iron (Fe+3/Fe+2). 5%Cu-5%Fe/ZrO2 not only displays the highest ibuprofen mineralization (83%) under optimum conditions but also exploits its activity in a wider range of pH (3–5) with extremely low metal leaching. The recycling of bimetallic catalysts reveals that only the 5%Cu-5%Fe/ZrO2 system is able to provide sustainable activity in heterogeneous Fenton process.

Enhancing iron redox cycling for promoting heterogeneous Fenton performance: A review

Conventional water treatment methods are difficult to remove stubborn pollutants emerging from surface water. Advanced oxidation processes (AOPs) can achieve a higher level of mineralization of stubborn pollutants. In recent years, the Fenton process for the degradation of pollutants as one of the most efficient ways has received more and more attention. While homogeneous catalysis is easy to produce sludge and the catalyst cannot be cycled. In contrast, heterogeneous Fenton-like reaction can get over these drawbacks and be used in a wider range. However, the reduction of Fe (III) to Fe(II) by hydrogen peroxide (H₂O₂) is still the speed limit step when generating reactive oxygen species (ROS) in heterogeneous Fenton system, which restricts the efficiency of the catalyst to degrade pollutants. Based on previous research, this article reviews the strategies to improve the iron redox cycle in heterogeneous Fenton system catalyzed by iron materials. Including introducing semiconductor, the modification with other elements, the application of carbon materials as carriers, the introduction of metal sulfides as co-catalysts, and the direct reduction with reducing substances. In addition, we also pay special attention to the influence of the inherent properties of iron materials on accelerating the iron redox cycle. We look forward that the strategy outlined in this article can provide readers with inspiration for constructing an efficient heterogeneous Fenton system.

Heterogeneous photo-Fenton oxidation of lignin of rice husk alkaline hydrolysates using Fe-impregnated silica catalysts

Present work shows results of a study on heterogeneous Fenton-like degradation of lignin alkaline hydrolysates formed in the process of obtaining a fibrous mass from rice husk. Fe-impregnate biogenic amorphous silica Fe/RH-SiO₂ obtained from rice husk was used as a catalyst. Using IR spectroscopy, X-ray diffraction and EDX analysis it was shown that iron(III) oxide in the form of hematite is present on the catalyst surface. Phenol was used for preliminary assessment of catalytic activity of the catalyst Fe/RH-SiO₂. The degree of degradation of phenol by the UV/visible radiation/Fe/RH-SiO₂/H₂O₂ system reaches 90%. The catalytic activity of Fe/RH-SiO₂ was studied in the reaction of lignin degradation of rice husk alkaline hydrolysates under ultraviolet and visible irradiation in the presence of hydrogen peroxide. The lignin solutions with COD: Н₂О₂ ratios from 1:2 to 1:16 were exposure under UV irradiation for 15-minute and the subsequent lightening on sunny days between 9 am and 8 pm in April for 7 days in the presence of a catalyst and without it. The catalyst concentration was 1.0 g L^-1. After that, it was found the content of phenolic compounds in the presence of a catalyst is 2-20 times lower than without it. The COD with the COD: Н₂О₂ = 1:16 ratio in the presence of a catalyst decreases 1.5 times as compared with the initial solution, whereas without a catalyst it increases 13 times.

Self-Assembled Nano-Fe3C Embedded in Reduced Graphene Oxide Aerogel with Efficient Fenton-Like Catalysis

Aiming at the removal of refractory organic pollutants in aqueous solution, self-assembled nano-Fe3C embedded in reduced graphene oxide (nano-Fe3C@RGO) aerogel was prepared by hydrothermal synthesis and high temperature treatment, and characterized by SEM, HRTEM, pore size distribution, XRD, XPS and FTIR. The results showed that the aerogel was porous, and most of the Fe3C particles were less than 100 nm in size. They were evenly dispersed and embedded in the RGO aerogel. Furthermore, the mapping images confirmed that the elements of carbon, nitrogen and iron were homogeneously distributed. Moreover, the specific surface area of the aerogel was up to 324.770 m2/g and most of the pore sizes were between 5 and 10 nm. The formation of nano-Fe3C was identified by XRD pattern and HRTEM. Analysis of an XPS spectrum indicates that the nano-Fe3C was embedded in the graphene layer. The aerogel contained a large number of functional groups, including -NH2-NH and -C=O, etc., which greatly strengthened the adsorption of organics. Finally, the Fenton-like catalytic degradation properties of the self-assembled nano-Fe3C@RGO aerogel were investigated by testing the removal of methyl orange from the aqueous solution. The results showed that the value of Ct/C0 decreased to 0.050 after 240 min, suggesting a high degradation rate was obtained. Meanwhile, the chemical reaction was verified in accordance with the first-order kinetic model, and the higher temperature was beneficial to the catalytic degradation. At the same time, methyl orange was degraded into small molecules by the hydroxyl and superoxide radicals generated during the reactions. Therefore, the self-assembled nano-Fe3C@RGO aerogel, as a novel Fenton-like catalyst, introduces a new approach in the field of treatment of refractory organic wastewater.

Coupling-oxidation process promoted ring-opening degradation of 2-mecapto-5-methyl-1,3,4-thiadizaole in wastewater

As an important raw material and intermediate of widely used antibiotics cefazolin and cefazedone, 2-mecapto-5-methyl-1,3,4-thiadizaole (MMTD) in antibiotic wastewater is hardly decyclized during wastewater treatment, posing great risk to the environment. This work proposed a green "coupling-oxidation" process to enhance ring-opening of MMTD during antibiotic wastewater treatment. In particular, the significant role of humic substances (HS) as pre-coupling reagent was emphasized. Real HS and different model HS, especially quinones, not only efficiently pre-coupled MMTD (>95%) but also promoted the MMTD removal by MnO₂ (from 72.4% to 92.4%). Mass spectrometric analysis indicated that MMTD pre-coupled to HS would be oxidized with ring opening to environmental-friendly sulfonated HS, while direct oxidation of MMTD produced MMTD dimers or sulfonated MMTD that would not undergo ring opening. Theoretical calculations indicated that pre-coupling to HS enabled the ring-opening oxidation by increasing the nucleophilicity and decreasing ring-opening barrier of thiadiazole. Based on the density function theory (DFT), the global nucleophilicity index (Nu) followed the trend of HS-MMTD > MMTD dimer > sulfonated MMTD, while the ring-opening barrier followed the trend of HS-MMTD (274 kJ/mol) < first ring of MMTD dimers (286 kJ/mol) < MMTD (338 kJ/mol). Theoretical calculations further confirmed that the cross-coupled HS-MMTD intermediate was more likely to be decyclized than intermediates from direct oxidation. Moreover, nitrogen, acetaldehyde group, sulfate and CO₂ were the products of thiadiazole ring degradation. Pre-coupling of MMTD with HS provides a new idea and strategy in developing a green and sustainable scheme for wastewater treatment.

Efficient phenol removal from petrochemical wastewater using biochar-La/ultrasonic/persulphate system: characteristics, reusability, and kinetic study

This research has analysed the physiochemical properties of a catalyst that has been developed - biochar-La, including BJH, BET, EDX, SEM, FTIR, pHpzc, and iodine number. The catalyst consisted of effective functional groups, including C=S, C-O, C=C, -COOH and O-H, with a specific surface area of 31.2 m²/g. The catalyst was used in the biochar-La/ultrasonic/persulphate system to remove phenol from wastewater. The kinetics, mechanism, and reusability of the catalyst for the phenol removal from synthetic wastewater were determined. The results suggested that phenol removal kinetics follows pseudo-first-order model (k = 0.0386 1/min), and the catalyst can be reused three times. The potential of operation of the biochar-La/ultrasonic/persulphate system - with the effective removal of phenol and other organic compounds from real petrochemical wastewater - was tested. The results indicated that the removal of phenol from the petrochemical wastewater with a relatively high total dissolved solid is >99%. The gas chromatography-mass spectrometry (GC-mass) test revealed that the complete decomposition of some contaminants in the petrochemical wastewater had occurred, as H₂O and CO₂ were detected. The contribution of a heterogeneous mechanism for phenol oxidation by biochar-La/ultrasonic/persulphate was calculated to be 60%. Overall, the results showed that the biochar-La/ultrasonic/persulphate system is very effective and promising for the removal of phenol from the petrochemical wastewater.

Enhanced catalytic activity of α-FeOOH-rGO supported on active carbon fiber (ACF) for degradation of phenol and quinolone in the solar-Fenton system

A new heterogeneous solar-Fenton catalyst, α-FeOOH-reduced graphene oxide (rGO) supported on active carbon fiber (ACF), was synthesized via in situ electrophoretic deposition in a self-assembly process. Optimization of the components (electrophoretic deposition time of GO and Fe, GO dosages), the effect of pH and the catalysts stability were investigated systematically. The results indicated that rGO-α-FeOOH composite is formed during the ferrous-ion-induced self-assembly process on ACF. FeOOH-rGO/ACF displayed excellent catalytic activity for degrading phenol and quinoline under the solar-driven photo-Fenton process in a wide range of pH values (4.5-9.5) and possess good stability in neutral condition. The phenol oxidation process on this catalyst was described by a pseudo-first-order kinetics model. Both the ACF support and solar irradiation promoted greater H₂O₂ decomposition and produced more OH radicals, thus, significantly improving the catalytic capacity. The introduction of graphene improved the catalytic capacity of the catalyst under solar irradiation. The optimal electrophoretic deposition time of GO and the optimal Fe and initial GO content in deposition were 10 min, 9.8 wt% and 15.0 wt%, respectively. The degradation pathways of phenol and quinoline in the solar-driven photo-Fenton process were also elucidated.

Comparative study of Cu-based bimetallic oxides for Fenton-like degradation of organic pollutants

In order to provide useful information for the rational design of effective Fenton-like catalyst, a series of Cu-based bimetallic oxides were synthesized and their Fenton-like performances for the degradation of Orange II and ciprofloxacin were compared. The structure, chemical oxidation state, surface charge property and redox ability of the catalysts were also investigated by different characterization techniques. Among them, NiCu exhibited the highest adsorption capacity towards Orange II and the highest activity for the production of OH from H₂O₂ decomposition, which could be attributed to its high surface area and highly positively charged surface. However, FeCu exhibited the highest activity for the degradation of Orange II. The reason might be that FeCu has more unpaired electrons and higher redox ability, thus promoting the activation of adsorbed Orange II through the electron transfer process. By contrast, NiCu exhibited the highest activity for the removal of ciprofloxacin because ciprofloxacin was mainly degraded by OH. Finally, the main degradation intermediates of Orange II and ciprofloxacin were determined by liquid chromatography-mass spectrometry.

Surface Facet of CuFeO2 Nanocatalyst: A Key Parameter for H2O2 Activation in Fenton-Like Reaction and Organic Pollutant Degradation

The development of efficient heterogeneous Fenton catalysts is mainly by "trial-and-error" concept and the factor determining H₂O₂ activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O-O bond in H₂O₂ is the key parameter determining the Fenton catalyst's activity. CuFeO₂ nanocubes and nanoplates with different surface facets of {110} and {012} are used to compare the effect of exposed facets on Fenton activity. The results indicate that ofloxacin (OFX) degradation rate by CuFeO₂ {012} is four times faster than that of CuFeO₂ {110} (0.0408 vs 0.0101 min^-1). In CuFeO₂ {012}-H₂O₂ system, OFX is completely removed at a pH range 3.2-10.1. The experimental results and theoretical simulations show that ^•OH is preferentially formed from the reduction of absorbed H₂O₂ by electron from CuFeO₂ {012} due to suitable elongation of O-O (1.472 Å) bond length in H₂O₂. By contrast, the O-O bond length is elongated from 1.468 to 3.290 Å by CuFeO₂ {110} facet, H₂O₂ tends to be dissociated into -OH group and passivates {110} facet. Besides, the new formed ≡Fe²⁺* on CuFeO₂ {012} facet can accelerate the redox cycle of Cu and Fe species, leading to excellent long-term stability of CuFeO₂ nanoplates.

Synthesis of different crystallographic FeOOH catalysts for peroxymonosulfate activation towards organic matter degradation

In this study, different crystalline structures of FeOOH have been prepared. α-FeOOH was synthesized through a hydrothermal method, whereas β-FeOOH was synthesized via a direct hydrolysis method. Moreover, γ- and δ-FeOOH were prepared by precipitation methods through slow and quick oxidation, respectively. On this basis, their crystal structure, morphology, and surface area were measured. Then, all the synthesized materials were applied to activate peroxymonosulfate (PMS) to generate sulfate radicals (SO₄⁻˙) for acid orange 7(AO7) degradation. Compared with α-FeOOH, β-FeOOH, and γ-FeOOH, δ-FeOOH showed more efficient decolorization of AO7 in the catalytic system because of its abundant surface area and crystalline structure. The effects of several parameters in the δ-FeOOH/PMS/AO7 system were investigated. The results show that the initial pH, which is related to the features of surface hydroxyl groups, is the decisive factor, and excellent catalytic activity is maintained in the pH range 5–8. The increase of catalyst dosage and appropriate increase of PMS concentration contributed to promote the degradation effect. However, self-quenching was observed in a high PMS concentration system. Moreover, δ-FeOOH was stable after six consecutive cycles, and the leaching of iron ions was negligible. According to the quenching test and electron spin resonance analysis, both SO₄⁻˙ and ˙OH were the dominant radicals for AO7 degradation.

In this study, different crystalline structures of FeOOH have been prepared.

A novel approach for recovery of metals from waste printed circuit boards and simultaneous removal of iron from steel pickling waste liquor by two-step hydrometallurgical method

Waste printed circuit boards (WPCBs) and steel pickling waste liquor (SPWL) have received extensive attention in recent years because of its harmfulness and resource. In this work, two-step leaching process was carried out by using SPWL as the leaching agent. A series of continuously domesticated bacteria were used for bioleaching and the bacterial strain was identified as Acidithiobacillus ferrooxidans (A. ferrooxidans) by 16S rDNA gene sequence analysis. The vast majority of the metals in WPCBs were recovered by two-step leaching, such as Cu, Pb, Zn, Sn, Al, Ni. Meanwhile, a large amount of iron was removed from SPWL, which greatly reduces the burden of the subsequent treatment. Pulp density and pH were optimized to achieve maximum recovery of copper and simultaneous removal of iron in bioleaching. It was found that the optimum conditions were pulp density 60 g/L and pH 0.5-1.0. Nearly 100% of copper was recovered and 51.94% of iron was removed under optimum conditions. The kinetic experiments showed that the rate of copper leaching was controlled by external diffusion rather than internal diffusion, because the acidic environment of the leachate prevented the formation of the precipitate and maintained it in a smaller size.

Visible-light photo-Fenton oxidation of phenol with rGO-α-FeOOH supported on Al-doped mesoporous silica (MCM-41) at neutral pH: Performance and optimization of the catalyst

In this study, α-FeOOH on reduced graphene oxide (rGO-α-FeOOH) supported on an Al-doped MCM-41 catalyst (RFAM) was optimized for the visible-light photo-Fenton oxidation of phenol at neutral pH. The stability of the catalysts, effect of bubbling aeration, and degradation intermediates were investigated. Results indicated that RFAM with a large Brunauer-Emmett-Teller (BET) area and mesoporous structure displayed excellent catalytic activity for the visible-light-driven (VLD) photo-Fenton process. Phenol degradation was well described by a pseudo-first-order reaction kinetics model. Raman analysis demonstrated that an rGO-α-FeOOH (RF) composite is formed during the ferrous-ion-induced self-assembly process. Al-MCM-41 could uniformly disperse RF nanosheets and promote the mobility and diffusion of matter. The activity of the main catalyst α-FeOOH was enhanced after the incorporation of rGO nanosheets. The α-FeOOH crystal in RFAM showed catalytic activity superior to those of Fe₃O₄ and Fe₂O₃. The RFAM catalyst, with an optimal GO-Fe²⁺mass ratio of 2.33, exhibited a larger BET area, pore size, and pore volume, and thus exhibited high performance and energy utilization efficiency in the VLD photo-Fenton reaction with remarkable stability. Bubbling N₂ inhibited catalytic performance, while bubbling O₂ or air only slightly accelerated the phenol degradation. Visible light played an important role in accelerating the formation of reactive oxygen species (·OH) for the highly efficient phenol degradation. Analysis of degradation intermediates indicated a high phenol mineralization level and the formation of low-molecular-weight organic acids. This work would be helpful in providing an insight into a new type of catalyst assembly and a possible route to a promising heterogeneous catalyst applicable in the visible light photo-Fenton process for effective wastewater remediation at neutral pH.