Visible Light-Driven Phenol Degradation via Advanced Oxidation Processes with Ferrous Oxalate Obtained from Black Sands: A Kinetics Study

Ferrous oxalate dihydrate (α-FOD) was synthesized from Ecuadorian black sands for phenol removal from aqueous solutions. Visible light-driven photodegradation kinetics were studied by varying the initial pollutant concentration, solution pH, and α-FOD dosage and by adding peroxydisulfate (PDS), including quenching tests. A representative model of phenol photodegradation was obtained by the Langmuir-Hinshelwood mechanism over a large range of concentrations (apparent kinetic constant, k = 0.524 h-1). Almost complete removal was reached within 1 h under dark + 9 h under visible irradiation. The degradation rate was slightly affected by pH in the range of 3 to 9, with a significant improvement at pH 11 (k = 1.41-fold higher). The optimal α-FOD dosage was ~0.5 g/L. Two regimes were observed when using PDS: first, a heterogeneous Fenton-like process during the first few minutes after PDS addition; second, pure photocatalysis to completely remove the phenol. When comparing the two systems, without and with PDS, the half-life time for pure photocatalysis was 2.5 h (after the lamp was switched on). When adding PDS (1.0 mM), the half-life time was reduced to a few minutes (5 min after PDS addition, phenol removal was 66%). The photocatalyst presented remarkable degradation efficiency up to five repeated cycles.

Synthesis of submicron ferrous oxalate from red mud with high Fenton catalytic performance on degradation of methylene blue

Ferrous oxalate dihydrate (FOD) can be used as a photo-Fenton catalyst with remarkable photo-Fenton catalytic and photocatalytic performances on organic pollutant degradation. Various reduction processes were compared in the current study to synthesize FODs from ferric oxalate solution utilizing the iron source in alumina waste red mud (RM), including natural light exposure (NL-FOD), UV light irradiation (UV-FOD), and hydroxylamine hydrochloride hydrothermal method (HA-FOD). The FODs were characterized and employed as photo-Fenton catalysts for methylene blue (MB) degradation, and the effects of HA-FOD dosage, H2O2 dosage, MB concentration, and the initial pH were investigated. The results show that HA-FOD has submicron sizes and lower impurity contents with more rapid degradation rates and higher degradation efficiencies compared with the other two FOD products. When using 0.1 g/L of each obtained FOD, 50 mg/L of MB can be rapidly degraded by HA-FOD by 97.64% within 10 min with 20 mg/L of H2O2 at pH of 5.0, while NL-FOD and UV-FOD achieve 95.52% in 30 min and 96.72% in 15 min at the same conditions, respectively. Meanwhile, HA-FOD exhibits strong cyclic stability after two recycling experiments. Scavenger experiments reveal that the predominant reactive oxygen species responsible for MB degradation are hydroxyl radicals. These findings demonstrate that submicron FOD catalyst can be synthesized using hydroxylamine hydrochloride hydrothermal process from ferric oxalate solution with high photo-Fenton degradation efficiency and reduced reaction time for wastewater treatment. The study also provides a new pathway of efficient utilization for RM.

Synergy of Adsorption and Photocatalytic Reduction for Efficient Removal of Cr(VI) with Polyvinylidene Fluoride@Polyvinyl Alcohol-FeC2O4/Bi2.15WO6

Although the photocatalytic reduction of Cr(VI) to Cr(III) by traditional powder photocatalysts is a promising method, the difficulty and poor recovery of photocatalysts from water hinder their wide practical applications. Herein, we present that FeC2O4/Bi2.15WO6 (FeC2O4/BWO) composites were tightly bonded to modified polyvinylidene fluoride (PVDF) membranes by chemical grafting with the aid of polyvinyl alcohol (PVA) to form photocatalytic composite membranes (PVDF@PVA-FeC2O4/BWO). The contact angle of PVDF@PVA-FeC2O4/BWO (0.06 wt % of FeC2O4/BWO) is 48.0°, which is much lower than that of the pure PVDF membrane (80.5°). Meanwhile, the permeate flux of 61.43 g m-2 h-1 and water flux of 250.60 L m-2 h-1 were observed for PVDF@PVA-FeC2O4/BWO composite membranes. The tensile strength of composite membranes reached 48.84 MPa, which was 9.8 times higher than that of PVDF membrane. It was found that the PVDF@PVA-FeC2O4/BWO membrane exhibited excellent photocatalytic Cr(VI) reduction performance under both simulated and real sunlight irradiation. The adsorption for Cr(VI) by PVDF@PVA-FeC2O4/BWO can reach 47.6% in the dark process within 30 min, and the removal percentage of Cr(VI) could reach 100% with a rate constant k value of 0.2651 min-1 after 10 min of light exposure, indicating a synergistic effect of adsorption and photoreduction for Cr(VI) removal by the composite membrane. The PVDF@PVA-FeC2O4/BWO membrane had good stability and reusability after seven consecutive cycles. Most importantly, the influences of foreign ions on Cr(VI) reduction were investigated to mimic real sewage, which revealed that no obvious adverse effects can be found with the presence of common foreign ions in sewage. The photocatalytic membrane material developed in this study provides a new idea for treating Cr(VI)-containing wastewater and has a more significant application prospect.

A facile synthesis of K3PMo12O40/WO3 crystals for effective sonocatalytic performance

Proper treatment of hazardous contaminants in the air, land, and water is crucial to environmental remediation. Sonocatalysis, by using ultrasound and suitable catalysts, has shown its potential in organic pollutant removal. In this work, K₃PMo₁₂O₄₀/WO₃ sonocatalysts were fabricated via a facile solution method at room temperature. Techniques such as powder X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy, and X-ray photoelectron spectroscopy were used to characterize the structure and morphology of the products. By using the K₃PMo₁₂O₄₀/WO₃ sonocatalyst, an ultrasound-assisted advanced oxidation process has been developed for the catalytic degradation of methyl orange and acid red 88. Almost all dyes were degraded within 120 min of ultrasound baths, proving that the K₃PMo₁₂O₄₀/WO₃ sonocatalyst has the advantage of speeding up the decomposition of contaminants. The impacts of key parameters, including catalyst dosage, dye concentration, dye pH, and ultrasonic power were evaluated to understand and reach optimized conditions in sonocatalysis. The remarkable performance of K₃PMo₁₂O₄₀/WO₃ in the sonocatalytic degradation of pollutants provides a new strategy for the application of K₃PMo₁₂O₄₀ in sonocatalysis.

Synthesis of porous iron hydroxy phosphate from phosphate residue and its application as a Fenton-like catalyst for dye degradation

Phosphate residue is a kind of hazardous solid waste and if not properly disposed of, could cause serious environmental contaminations. The abundant iron salt available in phosphate residue can be used to prepare photo-Fenton catalytic reagent for wastewater treatment. In this study, the phosphate residue was effectively purified by a hydrothermal recrystallization method, reaching an iron phosphate purity of 94.2%. The particles of iron phosphate were further processed with ball milling with their average size reduced from 19.4 to 1.6 μm. By hydrothermal crystallization of iron phosphate and thermal decomposition of oxalate precursor, porous iron hydroxy phosphate was prepared. The modified porous iron hydroxy phosphate (m-PIHP) of higher surface area with iron oxalate on its surface can degrade 98.87% of Rhodamine B in 15 min. Cyclic experiment showed that the catalyst still had a good catalytic activity after six cycles (>40%). The X-ray photoelectron spectroscopy results showed that the iron oxalate complex on the catalyst surface decomposed to produce ferrous ions and accelerated the rate of •OH production. The current work demonstrated that the m-PIHP synthesized from phosphate residue and modified with iron oxalate can be used as an effective dye wastewater treatment agent.

Anodic Activity of Hydrated and Anhydrous Iron (II) Oxalate in Li-Ion Batteries

We discuss the applicability of the naturally occurring compound Ferrous Oxalate Dihydrate (FOD) (FeC2O4·2H2O) as an anode material in Li-ion batteries. Using first-principles modeling, we evaluate the electrochemical activity of FOD and demonstrate how its structural water content affects the intercalation reaction and contributes to its performance. We show that both Li0 and Li+ intercalation in FOD yields similar results. Our analysis indicates that fully dehydrated ferrous oxalate is a more promising anodic material with higher electrochemical stability: it carries 20% higher theoretical Li storage capacity and a lower voltage (0.68 V at the PBE/cc-pVDZ level), compared to its hydrated (2.29 V) or partially hydrated (1.43 V) counterparts.

One-dimensional metal-organic frameworks for electrochemical applications

Metal-organic frameworks (MOFs) are as a category of crystalline porous materials. Extensive interest has been devoted to energy storage and energy conversion applications owing to their unique advantages of periodic architecture, high specific surface area, high adsorption, high conductivity, high specific capacitance, and high porosity. One-dimensional (1D) nanostructures have unique surface effects, easily regulated size, good agglutination of the substrate, and other distinct properties amenable to the field of energy storage and conversion. Therefore, 1D nanostructures could further improve the characteristic properties of MOFs, and it is of great importance for practical applications to control the size and morphological characteristics of MOFs. The electrochemical application of 1D MOFs is mainly discussed in this review, including energy storage applications in supercapacitors and batteries and energy conversion applications in catalysis. In addition, various synthesis strategies for 1D MOFs and their architectures are presented.

Oxalic acid modified copper tailings as an efficient adsorbent with super high capacities for the removal of Pb2

Comprehensive utilization of tailings is not only conducive to ensuring the sustainable use of resources but also can reduce the related environmental pollution. In the present work, a new utilization way of copper tailings was proposed and a novel composite (OMT-6) was prepared by modification of tailings with oxalic acid. The composite had super high Pb²⁺ adsorption capacity with the maximal Pb²⁺ removal capacity of 862.07 mg/g. Its Pb²⁺ removal behaviours followed pseudo-second-order kinetic equation and Langmuir model, suggesting that Pb²⁺ removal depended on monolayer adsorption. The surface of OMT-6 was rough and a lot of nanospheres were loaded on its surface. The composite had mesoporous structure and a larger specific surface area compared with tailings, the above characteristics of which facilitated Pb²⁺ removal. The major crystal structures of OMT-6 were transformed to CaC₂O₄•H₂O and FeC₂O₄•2H₂O after oxalic acid modification and Pb²⁺ could be removed by the ions exchange between Ca²⁺, Fe²⁺ and Pb²⁺. Pb²⁺ removal mechanisms of OMT-6 involved ion exchange, surface complexation and electrostatic attraction interaction, among which ion exchange played a key role. These results indicated that the prepared OMT-6 composite from copper tailings was an ideal material for Pb²⁺ removal from aqueous solution.

Active metal single-sites based on metal–organic frameworks: construction and chemical prospects

Metal single-point is a novel and potential design strategy that has been applied for the development of metal organic frameworks.

High adsorption capacity and super selectivity for Pb(Ⅱ) by a novel adsorbent: Nano humboldtine/almandine composite prepared from natural almandine

This study firstly reported a novel nano humboldtine/almandine composite (NHLA composite) prepared directly from almandine through one-pot method based on the interaction of almandine and oxalic acid. The formation of humboldtine/almandine binary phase from natural almandine was determined by X-ray diffraction. Analysis of scanning & transmission electron microscope showed that large amount of nano humboldtine with uniform size (average size of 15.59 nm) were loaded on the almandine sheets. Compared with raw minerals, Pb(Ⅱ) removal capacity of synthesized composite was significantly increased, demonstrating that the main active ingredient for Pb(Ⅱ) removal was humboldtine phase rather than almandine itself. Pb(Ⅱ) adsorption capacity was increased with the increasing of initial pH value or temperature. Langmuir isotherm and Pseudo-second order kinetic equation were well fitted with experimental results and the maximum Pb(Ⅱ) adsorption capacity from Langmuir isotherm was 574.71 mg/g at temperature of 25 °C. In addition, heavy metal removal experiments in coexisting systems of multiple heavy metal ions manifested that the composite had a high selectivity for Pb(Ⅱ) adsorption. Ion exchange, surface complexation and electrostatic interaction have involved in the Pb(Ⅱ) adsorption. The synthesized composite was considered as a low cost, high efficiency, super selectivity and easy to mass production material for Pb(Ⅱ) adsorption from solution.

Solid-Phase Microwave Reduction of WO3 by GO for Enhanced Synergistic Photo-Fenton Catalytic Degradation of Bisphenol A

The synergistic photocatalytic Fenton reaction is a powerful advanced oxidation technique for the degradation of persistent organic pollutants. However, microwave-induced thermal effects on the formation of novel structures facilitating the photocatalytic degradation have been rarely reported. Herein, a two-step microwave thermal strategy was developed to synthesize a new hybrid catalyst comprising defective WO_3-x nanowires coupled with reduced graphene oxides (rGOs). Conventionally, microwave methods could induce superhot spots on the GO surface, resulting in the site-specific crystallization and oriented growth of WO₃. However, in the solid phase, localized microwave thermal effects could reduce the interfacial area between WO₃ and rGO and enhance the bonding between them. As for the unique structure and surface properties, the synthesized catalyst enhanced the light absorption, promoted the interfacial charge separation, and increased the carrier density in the photocatalytic processes. In addition, surface formation of W⁴⁺ provided a new pathway for Fe³⁺/Fe²⁺ cycling which linked the photocatalytic reaction and the Fenton process. The optimized catalyst exhibited a remarkable performance in the degradation of bisphenol A with a ∼83% removal yield via a photo-Fenton route. These microwave-induced functionalities of materials for synergistic reactions could also give a new avenue to other photoelectrocatalytic fields and solar cells.

A novel composite of SiO2 decorated with nano ferrous oxalate (SDNF) for efficient and highly selective removal of Pb2+ from aqueous solutions

Developing a material with high adsorption capacity and selectivity to remove lead from Pb²⁺ polluted wastewater is of vital importance for environment protection and resources utilization. In this study, a novel composite, SiO₂ decorated with nano ferrous oxalate (SDNF), was prepared from natural biotite containing ores to remove Pb²⁺. Pseudo-first-order kinetic (R² = 0.99) and Langmuir models (R² = 0.99) fitted the data well, manifesting that Pb²⁺ adsorption process was monolayer adsorption. The maximum Pb²⁺ adsorption capacity was identified as 446.98 mg/g. SEM and TEM images showed that nano ferrous oxalate with average size of 11.51 nm was coated on the surface of ores, and their distributions were uniform. Results of XRD, XPS, FTIR and zeta potential indicated that ion exchange, surface complexation and electrostatic attraction interaction were involved in the remvoal of Pb²⁺, and the ion exchange between Fe²⁺ and Pb²⁺ played a major role. Moreover, both Cd²⁺ and Zn²⁺ removal efficiency are less than 2 % in Pb-Cd or Pb-Zn coexisted solution, indicating the composite possessed high selectivity for Pb²⁺ removal. All above results indicated that the composite was a material with high adsorption capacity and selectivity for Pb²⁺, which was suitable for remediation of Pb²⁺ pollution from Pb²⁺ containing wastewater.

A novel composite of almandine supported humboldtine nanospheres, in situ synthesized from natural almandine, possesses high removal efficiency of Cr(Ⅵ) over a wide pH range

Preparing a cost-effective material which can been applied in a wide pH range is very crucial for the remediation of Cr(Ⅵ) polluted water. In this study, a novel material, almandine/humboldtine nanospheres (AHN) composites, was synthesized directly from almandine by one-pot method. Characterizations of XRD and SEM/TEM showed that the structure changes of almandine to nano-humboldtine leaded to significant increase of Cr(Ⅵ) removal capacities. And 96.45% of Cr(Ⅵ) was removed by AHN-24 composite at pH value of 3, initial Cr(Ⅵ) concentration of 20 mg/L, temperature of 298.15 K and dosage of 0.6 g/L. Furthermore, Cr(Ⅵ) removal capacity was only decreased from 48.23 mg/g to 34.33 mg/g when the initial pH value increased from 3 to 11, which demonstrated that the synthesized composite had a wide pH application range in Cr(Ⅵ) removal. The thermodynamic parameters (ΔG⁰ < 0, ΔH⁰ > 0 and ΔS⁰ > 0) illustrated that Cr(VI) removal process was spontaneous and endothermic. FTIR and XPS revealed that the Cr(Ⅵ) removal mechanisms included reduction-precipitation and reduction-complexation. Combined with cost analysis, all of results implied that the synthesized composites were a high efficient and low cost material for Cr(Ⅵ) pollution remediation in a wide pH range.

Synergistic photocatalysis–Fenton reaction for selective conversion of methane to methanol at room temperature

Combining the photocatalysis and Fenton reaction highly promote the yield and selectivity of CH₃OH from CH₄ with solar light at room temperature, up to 471 μmol g⁻¹ h⁻¹ and 83%, respectively.