Wet Oxidation Research Articles

Optimal carbofuran degradation via CWPO in NOM-doped water by a framework Cu-doped aluminate perovskite catalyst derived from aluminum saline slags

This study is the first to propose the synthesis of LayAl1–xCuxO3–δ perovskite catalysts using Al recovered from acid leaching of saline slags. The effect of parameters such as the La/Al molar ratio was explored during the synthetic process. A suite of characterization techniques—including XRF, XRD, N2 adsorption, H2-TPR, FTIR, TGA-DTA, TEM, SEM, EDX, and XPS—confirmed the successful synthesis of high-purity (up to 90 %) perovskites with La and O vacancies, and a high concentration of Cu(I) active sites dispersed within the perovskite lattice. The best catalyst was used to optimize the degradation of carbofuran (CBF) in water doped with synthetic dissolved natural organic matter (NOM) using the Fenton-like catalytic wet peroxide oxidation (CWPO) approach. The effects of catalyst concentration, H2O2 dose, and pH on catalytic performance were investigated. Degradation, mineralization (COD removal), and H2O2 consumption were maximized, while Cu leaching was minimized using a statistical desirability function for multiple responses. Optimal conditions were found to be a catalyst concentration (mg Cu/mg H2O2) of 0.234 (2.0 g L–1), an H2O2 dose of 73.3 % (0.73 times the stoichiometric dose for full COD mineralization), and a remarkable circumneutral pH of 6.2. Under these conditions, degradation reached 94.1 %, and COD mineralization was 51 % under room temperature. Notably, the perovskite catalyst exhibited remarkable stability during reuse in up to three cycles, as demonstrated by the low Cu leaching (<1.30 mg L–1).

Simultaneous degradation of cyanobacteria and cyanotoxins by catalytic wet peroxide oxidation: Impact of morphology and growth stage

The widespread proliferation of potentially toxic cyanobacteria in source waters for drinking water treatment plants (DWTPs) presents a pressing contemporary challenge. Although catalytic wet peroxide oxidation (CWPO) has been recognized as a highly effective and environmentally friendly technology for removing cyanotoxins from water, the simultaneous degradation of cyanobacteria and cyanotoxins has been scarcely investigated. Considering their great morphological diversity, in this work, the impact of the presence of pure strains of several species of toxic and non-toxic cyanobacteria on the degradation of relevant cyanotoxins has been evaluated considering also the main stages of their life cycle. In each studied scenario, achieving a full eradication of the cyanobacteria also led to the complete elimination of the cyanotoxin, including both intra and extracellular fractions. Morphological factors, including filament and cell sizes, play a crucial role in the efficiency of the process. Small cells and long filaments entail a higher presence of particulate organic matter, which consumes hydroxyl radicals considerably in competence with the cyanotoxin degradation. Moreover, the growth stage emerges as a pivotal factor in understanding the CWPO process performance, with cyanobacteria in their early life stages, exhibiting more pronounced interference compared to later stages, probably due to their higher cell viability and accelerated metabolism. All these understandings are essential for the successful implementation of the technology in treating surface waters affected by toxic cyanobacterial blooms.

Mitigating Microfiber Pollution in Laundry Wastewater: Insights from a Filtration System Case Study in Galle, Sri Lanka

Synthetic fibers are widely used in daily life due to their durability, elasticity, low cost, and ease of use. The textile industry is the primary source of synthetic microfibers, as these materials are mostly used in production processes. Globally, plastic pollution has been identified as a major environmental threat in this era, since plastics are not degradable but break down into smaller particles such as mesoplastics, microplastics, and microfibers. Synthetic microfiber pollution is a significant issue in aquatic ecosystems, including oceans and rivers, with laundry wastewater being a major source. This problem is particularly pressing in cities like Galle, Sri Lanka, where numerous tourist hotels are located. Despite the urgency, there has been a lack of scientific and systematic analysis to fully understand the extent of the issue. This study addresses this gap by analyzing the generation of microfibers from laundry activities at a selected hotel and evaluating the efficiency of a laundry wastewater filtration system. This study focused on a fully automatic front-loading washing machine (23 kg capacity) with a load of 12 kg of polyester–cotton blend serviettes (black and red). Samples (1 L each) were taken from both treated and untreated wastewater during four wash cycles, with a total of 100 L of water used for the process. The samples were filtered through a 100 μm sieve and catalytic wet oxidation along with density separation were employed to extract the microfibers, which were then collected on a membrane filter paper (0.45 μm). Microfibers were observed and analyzed for shapes, colors and sizes under a stereo microscope. Results revealed that untreated laundry wastewater contained 10,028.7 ± 1420.8 microfibers per liter (n = 4), while treated wastewater samples recorded 191.5 ± 109.4 microfibers per liter (n = 4). Most of the microfibers observed were black and white/transparent colors. Further analysis revealed that 1 kg of polyester–cotton blend fabric can generate 336,833 microfibers per wash, which was reduced to 6367 microfibers after treatment. The filtration unit recorded an impressive efficiency of 98.09%, indicating a remarkably high capacity for removing microfibers from wastewater. These findings highlight the potential of such filtration techniques to significantly reduce microfiber emissions from laundry wastewater, presenting a promising approach to mitigating environmental pollution from microfibers.

Oxidation anisotropy of 4H-SiC wafers during chemical-mechanical polishing

4H silicon carbide (4H-SiC) wafers are widely used in high-power, high-temperature, and high-frequency electronics owing to their excellent physical and electrical properties. In the processing of 4H-SiC wafers, chemical-mechanical polishing (CMP) is commonly employed to realize atomic-scale smoothness, damage-free surface, and global planarization. The CMP process is the synergy of wet oxidation and mechanical grinding, whose efficiency significantly relies on the oxidation process. Therefore, understanding the wet oxidation mechanism of Si face and C face of 4H-SiC wafers is critical to high-efficiency double-side CMP. In this work, the anisotropic CMP performance of Si face and C face of 4H-SiC wafers are investigated. It has been found that the material removal rate of the C face is 2–3 times that of the Si face. The thicknesses of the transient oxide layer on the C face and Si face are 8.71 nm and 3.50 nm, respectively. X-ray photoelectron spectroscopy analysis reveals that the oxygen content on the C face is higher than that on the Si face after wet KMnO4 oxidation. This indicates that the C face of 4H-SiC is easier to oxidize, which results in more oxides that that on the Si face of 4H-SiC. Our work shows that accelerating the oxidation of the Si face of 4H-SiC wafers during the simultaneous double-sided CMP process is crucial for the efficient polishing of 4H-SiC wafers.

Exploring Topochemical Oxidation Reactions for Reversible Tuning of Thermal Conductivity in Perovskite Fe Oxides.

We present a study on the reversibility of thermal conductivity in iron oxides through topochemical oxygen exchange between brownmillerite (BM) (Ca,Sr)FeO2.5 and perovskite (PV) (Ca,Sr)FeO3.0. By using different oxidation methods, including gas phase (O2/O3), liquid phase (NaOCl in H2O), and solid electrolyte (Y2O3:ZrO2), we demonstrate that the oxidation pathway has a critical influence on the reversibility of the ionic-exchange process. Cyclic oxidation and reduction using O2/O3 or NaOCl lead to an important accumulation of structural defects, undermining the reversibility of thermal conductivity. In the case of wet oxidation, we demonstrate an inherent tendency of negative charge-transfer oxides toward amorphization and elucidate the origin of this effect. Conversely, the electrochemical injection of the O2- ions via a Y2O3:ZrO2 solid electrolyte reduces structural damage significantly, enhancing both reversibility and durability. This study underscores the importance of selecting appropriate topochemical oxygen exchange methods to maintain structural integrity and optimize functional performance in oxide-based tunable devices.

Convert food waste into easily biodegradable liquid substrate: New insights into wet oxidation as a pretreatment for anaerobic digestion

This study is the first comprehensive investigation into the industrial application of wet oxidation (WO) for food waste (FW) valorization. We analyzed the physicochemical properties of WO products and performed a material flow analysis. WO achieved a 25.7 % reduction in chemical oxygen demand and produced liquid and solid products suitable for high-value applications. The liquid product featured high biodegradability (B/C ratio of 0.65), significant BOD5 (33 ± 9 g/L), low total solids (3.5 % ± 0.4 %), and low metal concentrations, making it ideal for high-efficiency anaerobic digestion or as a carbon source in wastewater treatment. The solid product, with a total solids content of 63.9 % ± 1.4 %, is a potential organic fertilizer alternative. Life cycle assessment showed that WO-related scenarios offered superior greenhouse gas (GHG) reduction compared to conventional anaerobic digestion (11.30 kg CO2-eq/t FW slurry). The most effective scenario, combining WO with a carbon source and organic fertilizer alternative, achieved a GHG reduction of −21.80 kg CO2-eq/t FW slurry. Consequently, this study demonstrates that WO, as a pretreatment for food waste valorization, is both technically feasible and environmentally sound, offering valuable engineering references for the implementation of high-efficiency anaerobic digestion processes for food waste.

Synergistic catalytic degradation of Methotrexate using Ce-based high-entropy metal oxides: Insights from DFT calculations and CWPO performance

Methotrexate (MTX), a widely used anticancer drug, is a refractory organic pollutant posing serious threats to ecosystems and human health. This study focuses on the development of a novel catalyst composed of Ce-based high-entropy metal oxides (NHEMO) supported on nepheline for the catalytic wet peroxide oxidation (CWPO) process, targeting MTX degradation in simulated wastewater. The NHEMO catalyst exhibited a unique high-entropy structure that enhances catalytic performance by facilitating diverse electronic interactions, which was confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showing a well-defined crystal structure and uniform dispersion of metal oxides. Additionally, X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) revealed a stable metal composition and high oxidation states of active metal sites. At a reaction temperature of 160 °C, with a residence time of 150 s and an oxidation coefficient of 5, the catalyst achieved a MTX removal rate of 93.49 % and a chemical oxygen demand (COD) removal of 99.95 %. Density Functional Theory (DFT) calculations further demonstrated that H2O2 decomposes into both adsorbed (surface-bound) and free (solution-phase) hydroxyl radicals (·OH). These radicals synergistically degrade MTX through both radical and non-radical pathways, ensuring comprehensive pollutant breakdown. The catalyst also showed excellent stability and a very low metal dissolution rate during the reaction, maintaining high catalytic activity after repeated recycling. This catalyst offers high cost-effectiveness, activity, and stability, providing a promising solution for treating refractory organic pollutants in pharmaceutical wastewater.

Sulfur oxidation of ferrate synthesized from sludge in the aspect of desulfurization: A parametric study

Abstract The emission of sulfur in the atmosphere poses a significant threat to human health and the environment. To address this issue, stringent regulations have been implemented to limit the sulfur content in diesel, and novel desulfurization technologies are being developed. One notable technology is oxidative desulfurization (ODS), which employs oxidants to transform sulfur compounds into their corresponding sulfones, which are relatively easier to recover. The application of high-shear mixing in ODS has been studied to increase sulfur-to-sulfone conversion by creating smaller droplets and reducing mass transfer resistance. This research investigates the application of potassium ferrate derived from drinking water treatment sludge (DWTS), in the mixing-assisted oxidative desulfurization (MAOD) of a dibenzothiophene (DBT) model fuel. Potassium ferrate was synthesized using the wet oxidation method. The study evaluated the effects of ferrate concentration (400 to 600 ppm), agitation speed (4,400 to 10,800 rpm), and temperature (40 to 60 °C) on the efficiency of DBT conversion. The results revealed that 493.2 ppm DBT conversion was achieved at 550 ppm Fe(VI) concentration, 7,600 rpm agitation speed, and 50 °C temperature. Notably, increasing Fe(VI) concentration, agitation speed, and temperature had significant effects on sulfur reduction. This study demonstrates the potential of using potassium ferrate derived from DWTS in MAOD for effective desulfurization and discusses insights into the effects of operating conditions to enhance desulfurization efficiency. Ultimately, the study contributes to the development of environmentally friendly and cost-effective desulfurization technologies.

The catalytic wet air oxidation of pharmaceutical wastewater with alkali-activated Mn and Cu composites: preparation of precursors by calcination of kaolin with Mn and Cu

In recent decades, the concentration of pharmaceutical residues and narcotics has increased in municipal wastewater. Decomposing these toxic organic chemicals is challenging and requires new techniques and advanced catalytic materials. Precursors of metal composites were prepared by calcining an aqueous suspension of natural clay–based kaolin with Mn and Cu, binding chemically the active metals to the aluminosilicate frame structure of the precursor. The specific surface area of Mn and Cu composite was 67 m2/g and 81 m2/g, respectively. The mechanical durability was determined in terms of compressive strength, and 3.3 MPa and 3.6 MPa were obtained, respectively. In the CWAO of pharmaceutical wastewater, Mn composite gave the highest conversions of 54% and 46% of the chemical oxygen demand (COD) and total organic carbon (TOC), respectively. Metal composites were mechanically and chemically highly durable, inducing only 1.2 wt.% and 1.4 wt.% mass loss. In CWAO, Mn and Cu composite increased the biodegradation of organic species in the wastewater by 65% and 75%, respectively.

Wet oxidation behavior of Al-Y synergistic modified liquid phase sintered SiC

The wet oxidation behavior of LPS-SiC ceramics as well as the synergistic modification effect of Al2O3 and Y2O3 as sintering aids are investigated. The results show that SiO2 oxide scale is transformed to aluminosilicate with the addition of Al2O3, which can inhibit the crystallization of oxide layer and formation of cracks. The aluminosilicate oxide layers have low kl value close to zero, which can reduce the consumption of protective oxide layer under water-containing atmosphere. Y2O3 are mainly transformed to Y2Si2O7 to resist the diffusion of oxidative gas. However, with the increase of sintering aids content, the aluminosilicate layer with excessive viscosity limits the emission of gas generated by oxidation and causes many bubbles left in oxide scale which provided rapid channel for oxidative gas. Therefore, LPS-SiC with lower content of sintering aids has better oxidation resistance. This work can provide guidance for the component design of SiC-based ceramics and composites.

Efficient access to non-damaging GaN (0001) by inductively coupled plasma etching and chemical–mechanical polishing

As third-generation semiconductors advance, gallium nitride (GaN)-based devices are gaining significant attention. However, the processing of GaN substrates directly affects device performance. This paper proposes an ICP etching-chemical–mechanical polishing (CMP) strategy to efficiently produce GaN single-crystal substrates with non-destructive, atomic-level surfaces. The process time is significantly reduced from 15 h to 1.5 h. The wet oxidation reaction during CMP eliminates impurities and defects from dry etching. FIB-STEM tests confirm that this method is non-destructive, as the ICP technique enables isotropic etching, and CMP introduces no new damage to the substrate. This approach enhances the productivity of large-size GaN single-crystal substrates, promoting their broader application in laser displays, RF devices, and power electronics.

A machine-learning interatomic potential to study dry/wet oxidation process of silicon

We developed an accurate and efficient machine learning potential with DFT accuracy and applied it to the silicon dry/wet oxidation process to investigate the underlying physics of thermal oxidation of silicon (001) surfaces. The accuracy of the potential was verified by comparing the melting point and structural properties of silicon, the structural properties of a-SiO2, and the adsorption properties on the silicon surface with experiment and DFT data. In subsequent thermal oxidation simulations, we successfully reproduced the accelerated growth phenomenon of the wet oxidation in the experiment, discussed the oxide growth process in detail, and elucidated that the accelerated growth is due to hydrogen in the system that both enhances the adsorption of oxygen on the silicon surface and promotes the migration of oxygen atoms. Finally, we annealed the oxidized structure, counted the defect information in the structure before and after annealing, and analyzed the defect evolution behavior during the annealing process.

Quantitative analysis of microplastics in beach sand via low-temperature solvent extraction and thermal degradation: Effects of particle size and sample depth

Quantifying trace levels of microplastics in complex environmental media remains a challenge. In this study, an approach combining field collection of samples from different depths, sample size fractionation, and plastic quantification via pyrolysis-gas chromatography–mass spectrometry (Py-GC–MS) was employed to identify and quantify microplastics at two public beaches along the northeast coast of the U.S. (Salisbury beach, MA and Hampton beach, NH). A simple sampling tool was used to collect beach sand from depth intervals of 0–5 cm and 5–10 cm, respectively. The samples were sieved to give three size fractions: coarse (>1.2 mm), intermediate (100 μm–1.2 mm), and fine (1.2 μm–100 μm) particles. Following density separation and wet peroxide oxidation, a low-temperature solvent extraction protocol involving 2-chlorophenol was used to extract polyester (PET), polystyrene (PS), polyamide (PA), and polyvinyl chloride (PVC). The extract was analyzed using Py-GC–MS for the respective polymers, while the solid residue was pyrolyzed separately for polyethylene (PE) and polypropylene (PP). The one-step solvent extraction method significantly simplified the sample matrix and improved the sensitivity of analysis. Among the samples, PET was detected in greater quantities in the fine fraction than in the intermediate size fraction, and PET fine particles were located predominantly in the surface sand. Similar to PET, PS was detected at higher mass concentrations in the fine particles in most samples. These results underscore the importance of beach environment for plastic fragmentation, where a combination of factors including UV irradiation, mechanical abrasion, and water exposure promote plastic breakdown. Surface accumulation of fine plastic particles may also be attributed to transport of microplastics through wind and tides. The proposed sample treatment and analysis methods may allow sensitive and quantitative measurements of size or depth-related distribution patterns of microplastics in complex environmental media.

Multi-criteria optimisation of subcritical wet oxidation for sludge treatment

Subcritical wet oxidation (SWO) is an environmentally-friendly solution for sewage sludge volume reduction. However, little study has comprehensively optimised SWO conditions across various aspects. This study developed a multi-objective model using genetic algorithms (GAs) to optimise SWO conditions, considering sludge deconstruction, emissions, energy balance, and resource recovery. The multi-criteria optimisation approach highlights the significant environmental benefits of SWO, including substantial sludge volume reduction and effective pollutant removal. An in-depth analysis of temperature, reaction time, and severity factor revealed their critical roles in enhancing sludge deconstruction and resource recovery efficiency. GAs predicted optimal conditions at 271 ± 2 °C and 51 ± 1 min, with confirmation experiments showing only 12% discrepancy between predicted and actual outcomes. This study provides practical insights for efficient sewage sludge treatment and sustainable wastewater management.

Impact of H2 Reduction on the Performance and Stability of Phenol Catalytic Wet Air Oxidation (CWAO) Over Cu−Ce/AC Catalysts

AbstractIn this study, we utilized the carbon precursor derived from walnut shells to synthesize a series of Ce‐modified Cu‐based carbon catalysts (Cu−Ce/AC) via the impregnation method. We investigated the performance and stability of Cu−Ce/AC catalysts for CWAO phenol after H2 reduction at various temperatures. The Cu−Ce/AC‐250 catalyst exhibited its highest performance at 250 °C, achieving complete phenol conversion. Characterization results from techniques including XRD, BET, FTIR, ICP‐OES, SEM‐EDS, XPS, and H2‐TPR indicated that the active components of the H2‐reduced catalysts were more evenly distributed across the catalyst surface, thereby enhancing the availability of reactive sites for phenol oxidation. Simultaneously, under the appropriate temperature, the H2 atmosphere can reduce a portion of the Cu2+ on the catalyst surface to Cu+, thereby mitigating the loss of Cu components.

The CuS-coated CuO nanostructures grown by ion exchange reaction for efficient photoelectrochemical water splitting

CuO is a promising solar photocathode for hydrogen production. However, it suffers serious photocorrosion in the electrolyte, which hinders the efficiency of photoelectrochemical (PEC) water splitting. In the study, Cu(OH)2 nanowires were in situ grown on copper foils through a straightforward wet chemical oxidation process, followed by annealing in air to synthesize CuO photocathode. To enhance their performance, the surface of CuO photocathode was modified by loading CuS with the ion exchange reaction (IER). Under AM 1.5 G, the CuO photocathode modified by CuS showed a significant improvement in the photo-current density, achieving the highest photo-current density was −4.83 mA·cm−2 at 0 V vs. RHE, which was far superior to the photo-current density (-2.02 mA·cm−2) of pristine CuO photocathode at the same potential. Furthermore, the maximum applied bias photon-to-current efficiency (ABPE) of the CuO/CuS photocathode is 0.77 %, which is superior to that of pristine CuO (0.24 %). The enhanced PEC performance of CuO/CuS photocathode is attributed to the improved light absorption and the efficient separation of photogenerated electron-hole pairs.

O2-H2O2 high-efficient co-oxidation of carbohydrate biomass to formic acid via Co3O4/C nanocatalyst

The conversion of biomass to chemicals/fuels has emerged as a valuable solution that offers both environmental and economic benefits, with the transformation of carbohydrate into formic acid garnering escalating scholar interest. However, the relative limited efficiency of catalyzed-oxidation or expensive cost of H2O2 and alkali in wet hydrothermal oxidation impose limitations on industrialization. This paper proposed a new idea for formic acid production by O2-H2O2 co-oxidation of carbohydrate. A two-step reaction method was developed, where the initial step is engineered to regulate the carbon chain cleavage of carbohydrates to augment the production of active intermediate. Oxygen was employed in the subsequent step as effective oxidant through free radical mechanism, resulting in a formic acid yield of 82.6%. Theoretical calculation, intermediates detection and real time EPR confirmed the reaction mechanism. Finally, the universality of the reaction was verified by using disaccharides and polysaccharides such as cellulose as substrates.

Rare earth elements sequestration in phytoliths: Partitioning patterns and influencing mechanism

Rare earth elements (REEs) are integral to numerous high-tech industries, yet their biogeochemical cycling within ecosystems remains inadequately characterized. Recently, phytoliths have been identified as potentially significant sinks for REEs; however, their role in the cycling of these elements has been underestimated. In this work, we investigate the accumulation of REEs in phytoliths (PhytREEs) within the Greater Khingan Mountains region, employing an optimized wet oxidation method combined with heavy liquid flotation to quantify PhytREEs contents in surface soils. The results revealed an elevation-dependent pattern of PhytREEs concentration, with heightened levels at higher altitudes and diminishing concentrations towards the eastern plains. The enrichment coefficient of PhytREEs (ECPhytREEs) was found to be approximately 2.7 %, indicative of a moderately selective sequestration process. The multivariate analysis indicated that terrain complexity, climatic patterns, soil texture, and organic matter significantly influence the uptake and storage of REEs in plants, subsequently affecting their partitioning in phytoliths. Among these factors, the complexation of REEs with organic matter emerged as a pivotal mechanism facilitating their immobilization within phytoliths. Soil characteristics also play a non-negligible role in modulating REEs dynamics. Our findings highlight the predominant influence of climate on PhytREE storage, suggesting that climatic variables are the primary drivers modulating the bioavailability and ultimate sequestration of REEs within phytoliths. This study enhances our understanding of the biotic-abiotic interplay in the sequestration of REEs and underscores the need to incorporate phytoliths into models of terrestrial REE cycling.

Treatment of Crude Phosphoric Acid Using Activated Carbon-Based Nanocomposites Integrated with Catalytic Wet Peroxide Oxidation

Treatment of Crude Phosphoric Acid Using Activated Carbon-Based Nanocomposites Integrated with Catalytic Wet Peroxide Oxidation

Performance of catalytic wet oxidation on thermochemical aqueous effluents assessed by FT-ICR MS

Aqueous phase (AP) is frequently observed in bio-oil from biomass thermochemical conversion or as an upgrading coproduct. However, AP contains high organic content that can be toxic and that must be reduced or removed to be then treated in existing wastewater plants. A promising method to upgrade these APs is the catalytic wet peroxide oxidation (CWPO) that was applied here on APs of both hydrothermal liquefaction and pyrolysis bio-oils from softwood and hardwood. Efficiency of the CWPO was assessed by investigating the molecular composition of raw and treated APs by ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI) in negative- and positive-ion modes. Combination of FT-ICR MS and multivariate statistical analyses evidenced efficiency of the process with new compounds resulting from the oxidative depolymerization, characterized by lower unsaturation degree and molecular weight, and higher oxygen atom count. Refractory compounds were also observed, which are notably characterized by high unsaturation degrees. Interestingly, both detection modes were shown to be complementary for the understanding of the CWPO process. ESI (-) allowed to assess the completion of the oxidation process in detecting carboxylic acid conversion products and to specifically evidence refractory products. ESI (+) was informative on the CWPO process, especially on the conversion of the basic compounds, with the decrease of the detected species. Eventually, softwood AP was shown to be more reluctant to CWPO than the hardwood one.