Wet Oxidation Research Articles

Microplastic contamination in rivers: a survey from the Nan River, Thailand

BackgroundSince the 1970s, microplastic contamination has been discovered in various environments. These emerging pollutants threaten water quality and freshwater ecosystems. We aimed to assess microplastic contamination in the Nan River by quantifying their presence, characterising their morphology, and identifying their polymer composition. MethodsThe survey was conducted along the Nan River in northern Thailand, which is divided into three distinct zones based on land use (ie, community areas, agricultural areas, and natural areas). A wide array of samples, including surface water, sediment, and specimens from five aquatic species—Barbonymus altus, Laides hexanema, Kryptopterus cryptopterus, Pomacea canaliculata, and Pseudodon cambodjensis cambodjensis—were collected. The presence of microplastics was analysed via the wet peroxide oxidation process for sample digestion, morphological characteristics were assessed through microscopic examination, and Fourier transform infrared spectrophotometry was used to identify the polymer composition of the microplastics. FindingsNatural areas had the highest mean concentration of microplastics in surface water (23·67 pcs/L, SD 14·22), whereas community areas had the highest mean concentration in soil sediment (24·67 pcs/g, 15·04). No statistically significant differences in the amounts of microplastics were observed among the various land-use zones. Microplastics were predominantly found in the gastrointestinal tracts of fish specimens, with varying quantities observed among different aquatic species; B altus had the highest concentration (11·80 pcs/g, 8·98). The primary microplastic shapes identified were filaments (53·99%), fragments (35·58%), and cylindrical forms (10·43%). We identified ten different polymer types, with polypropylene, nylons, and polymethyl methacrylate being the most prevalent among them. InterpretationAnalysing microplastic pollution in this area brings attention to the issues affecting the rivers of Thailand and emphasises ecological risks, particularly microplastic presence in aquatic species. Because of the Nan River's ecological importance, we call for increased research and collaboration to address the increasing threat of microplastic pollution. FundingNaresuan University.

Formation of secondary microplastics during degradation of plastics originating from the MV X-Press Pearl maritime disaster

AbstractThe MV X-Press Pearl maritime incident had a profound impact on the marine and coastal ecosystems along the west coast of Sri Lanka. Considerable quantities of plastic pellets, specifically nurdles or pellets measuring less than 5 mm and estimated at 1680 tonnes, were released into the Indian Ocean. A notable portion of these plastic pellets/primary microplastics (MPs), has the potential to degrade into secondary MPs. The objective of this study was to investigate and understand the degradation process of plastic pellets into secondary MPs under the extreme conditions of fire and exposure to chemicals during the MV X-Press Pearl maritime disaster. Beach sand samples were collected from 40 locations along the affected west coast of Sri Lanka, at both mean sea level and the berm. An additional 20 samples were collected for a background study covering the entire coastline of Sri Lanka. The Wet Peroxide Oxidation (WPO) process was employed to separate microplastics, and observations of secondary MP quantities were recorded. Fourier Transform Infra-Red Spectroscopic (FTIR) analysis was carried out to identify functional groups of MPs. The variance in average values of secondary MPs at mean sea level (large MPs (i.e. size > 0. 5 mm) = 33 ± 56 items per 1 mm2 and total MPs (i.e. observed through microscope under 40× magnification) = 61 ± 66 items per 1 mm2) and the berm (large = 61 ± 154 items per 1 mm2 and total MPs = 106 ± 165 items per 1 mm2) suggested significant dispersal of large quantities of MPs to other areas in the Indian Ocean with oceanic currents. The baseline average value of secondary total MPs in other coastal areas of the country was approximately 53 ± 66 items per 1 mm2. The positive correlation between large and total secondary MPs and plastic pellets pollution index indicates that a considerable amount of plastic pellets were degraded into secondary MPs within 6 to 8 days after the accident, under the influence of nitric acid and heat/fire. These secondary MPs are mainly composed of low-density polyethylene (LDPE) and linear low-density polyethylene (LLDPE), as identified by FTIR observations. Consequently, these lightweight polymers have the potential to spread across a wider region, posing a severe environmental threat on a global scale as a transoceanic marine pollutant.

Wet peroxide oxidation process catalyzed by Cu/Al2O3: phenol degradation and Cu2+ dissolution behavior.

Catalytic wet peroxide oxidation (CWPO) has become an important deep oxidation technology for organics removal in wastewater treatments. Supported Cu-based catalysts belong to an important type of CWPO catalyst. In this paper, two Cu catalysts, namely, Cu/Al2O3-air and Cu/Al2O3-H2 were prepared and evaluated through catalytic degradation of phenol. It was found that Cu/Al2O3-H2 had an excellent catalytic performance (TOC removal rate reaching 96%) and less metal dissolution than the Cu/Al2O3-air case. Moreover, when the organic removal rate was promoted at a higher temperature, the metal dissolution amounts was decreased. Combined with hydroxyl radical quenching experiments, a catalytic oxidation mechanism was proposed to explain the above-mentioned interesting behaviors of the Cu/Al2O3-H2 catalyst for CWPO. The catalytic test results as well as the proposed mechanism can provide better guide for design and synthesis of good CWPO catalysts.

Catalytic wet peroxide oxidation of organic dye with in-situ generated H2O2 over bifunctional Fe-Pt@Pd/SiO2 catalyst prepared by double-metal complex salt approach

While the Fenton reaction is efficient in wastewater treatment, the intrinsic problem of the dosage-dependent process poses another burden on ecosystem. Herein, we propose a highly efficient and environmentally-benign catalytic wet peroxide oxidation (CWPO) of methyl orange (MO) using in-situ generated H2O2 from hydrogen and air instead of ready-made H2O2. Pt@Pd/SiO2 and Pd@Pt/SiO2 catalysts were prepared by double-metal complex salt approach, and they were combined with soluble Fe salt (CWPO-I) or impregnated Fe (CWPO-II). The MO degradation rate of Pt@Pd/SiO2 for CWPO-I was 2.5 times faster than that of the conventional PdPt/SiO2. This can be rationalized in terms of Pd-enriched surface with strong interaction between Pt and Pd. Moreover, bifunctional Fe-Pt@Pd/SiO2 catalyst demonstrated outstanding activity in promoting CWPO-II with in-situ generated H2O2, even outperforming its counterpart with ready-made H2O2. This new approach offers an efficient water remediation method free from addition and generation of any undesirable chemicals affecting environment.

Application of catalytic wet peroxide oxidation for sunscreen agents breakdown

Sunscreen agents are chemical compounds widely used nowadays for skin protection from UV sunlight. Recently, their ubiquitous occurrence in aquatic systems has been evidenced, which poses a high risk for the environment and human health as they are associated with endocrine disrupting activity, reproductive toxicity, and genotoxicity. In this work, the feasibility of an economically and environmentally friendly catalytic system based on the thermally modified natural magnetite and hydrogen peroxide (Fe3O4-R400/H2O2), has been evaluated for the degradation of two representative sunscreen agents: benzophenone-3 (BP-3) and 4-aminobenzoic acid (PABA) in wastewater. The experiments were conducted under circumneutral pH (pH0 = 5), with temperature control (25 °C). Both compounds (500 μg L−1) were successfully removed from water by using a relatively low catalyst concentration (0.5 g L−1) and the theoretical stoichiometric H2O2 dose for their complete oxidation (∼2.3 mg L−1). Afterwards, a complete operating condition study was performed with BP-3, given its predominant occurrence in fresh waters, analysing the influence of H2O2 dose (1.2–4.6 mg L−1), catalyst concentration (0.1–0.5 g L−1), and temperature (25–45 °C). From the evolution of the identified by-products, a reaction pathway was proposed according to which oxidation of BP-3 gives rise to several aromatic intermediates, which finally evolve to short-chain organic acids. The generation of such aromatic by-products led to a considerably ecotoxicity increase in the initial stages of the reaction, but non-toxic effluents were ultimately achieved. Notably, the mineralization yield reached was above 60%. As a proof of concept, the feasibility of the system was finally demonstrated in real water matrices (WWTP effluent and surface water).

Assessment of Microplastics in Hanumante River of Kathmandu Valley

Plastic debris is one of the most significant organic pollutants in the aquatic environment. Researchers are currently focusing on the impact of micro and nano-scale plastic waste on aquatic systems. In this study, we investigated the distribution of plastic pellets and fragments present in the freshwater ecosystem. The goal was to assess microplastic (MP) abundance in the Hanumante River, a tributary of the Bagmati River, and analyze their properties. Sample collection involved the bottle sampling method. Filtration, wet peroxide oxidation, density separation, gravimetric analysis, and microscopic examination were performed to study the characteristics of microplastics. The study was conducted by following the guidelines of the National Oceanic and Atmospheric Administration (NOAA) protocol. Gravimetric analysis was applied to calculate the reduced mass of the sample after total organic carbon reduction. Results showed that the maximum amount of reduced sample was obtained from the sample taken from sample taken from Madhyapur Thimi area (~3.593g) and the minimum amount of reduced sample was obtained from the sample taken from the Shiva temple Jagati area (~2.130g). Microscopic inspection showed that samples taken from different locations were composed of an average of 14–23 microplastics per liter of sample. FT-IR analysis was performed to analyze the characteristics of microplastics and the type of polymers present in the sample which showed the abundance of polymer materials like polyethylene, polypropylene, and polycarbonates. The findings imply that appropriate plastic waste management measures be implemented in the communities to safeguard the ecosystem benefits derived from the river.

Prospects of industrial membrane concentrates: treatment of landfill leachates by coupling reverse osmosis and wet air oxidation.

Stabilized landfill leachates are characterized by a high chemical oxygen demand and limited biodegradability. This study investigates the removal of the organic fraction (chemical oxygen demand and total organic carbon) using a treatment approach that couples membrane processes and wet air oxidation (operating at 200-300 °C and 18 MPa). The aim is to address the challenges posed by landfill leachate membrane concentrates considering variations throughout the year across three different seasons. The efficiency of the treatment path was assessed through the removal of the chemical oxygen demand and total organic carbon, with additional insights provided by fluorescence spectroscopy to evaluate the degradation of the organic compounds' complexity. The most favorable results were achieved at the highest temperature (300 °C) with removals over 90% for total organic carbon and 87% for chemical oxygen demand, along with a complete elimination of fluorescence. The coupling of membrane processes and wet air oxidation has demonstrated its effectiveness in degrading the organic compounds of landfill leachates. The overall mass balance on the treatment path indicates the feasibility of discharging the treated effluent into the environment, meeting regulatory thresholds for total organic carbon and chemical oxygen concentrations.

Valorisation of waste activated sludge for protease production by Bacillus licheniformis

Waste activated sludge (WAS) is the main by-product of wastewater treatment plants. Its management is considered one of the major environmental challenges worldwide, due to the large volume generated, along with the presence of pathogens and hazardous substances. Nevertheless, the biopolymers present in its structure can make it a promising source of nutrients to obtain high value-added products. Therefore, this study is focused on the use of WAS as a renewable feedstock to produce proteases by Bacillus licheniformis. To this end, both thermal hydrolysis (TH) and wet oxidation (WO) were evaluated as strategies for the solubilization of the valuable compounds. The results revealed that an operation time of 90 min (at 140 °C) was optimal for both pretreatments, which allowed obtaining concentrations of carbohydrates, proteins and humic acids up to 2.7 ± 0.1 g/L, 5.3 ± 0.1 g/L and 5.1 ± 0.1 g/L, respectively. Regarding bioconversion processes, the initial pH of the medium significantly influenced the assimilation of the biopolymers, bacterial growth and enzyme biosynthesis. In this sense, a pH of 5.5 for the WAS pretreated by TH (WAS-TH) and 7.5 for the WAS pretreated by WO (WAS-WO) allowed maximizing the proteolytic activities, reaching values of 767 ± 2 U/mL and 838 ± 6 U/mL, respectively. Additionally, higher initial inoculation levels positively influenced the performance of the fermentative process. Consequently, a 30 % inoculum resulted in enzymatic activities of 828 ± 11 U/mL for WAS-TH and 903 ± 4 U/mL for WAS-WO. Partial purification of the medium with ammonium sulphate increased the enzymatic activity by 7 times for WAS-TH and 3 times for WAS-WO.

Novel synthesis, characterization, and application of calcium ferrate (VI) in water treatment

Poor raw water quality has led science and technology research to explore more environmentally friendly water treatment methods, such as advanced oxidation processes. Ferrate (VI) salts have been regarded as a new green oxidant, cost-effective, and coagulant/flocculent in a single mixing and dosing unit in wastewater treatment. This research aimed to synthesize calcium ferrate (CaFeO4), a benign green chemical that can be utilized to treat water and wastewater through a facile wet oxidation process, with minimal increase in electrical conductivity. This study used the wet oxidation approach to synthesize stable aqueous calcium ferrate in an alkaline media using distilled water. During process optimization, CaFeO4 was synthesized and named 60-CaFeO4, 70-CaFeO4, 80-CaFeO4, and 90-CaFeO4, where the numbers represent the synthesis temperature. The prepared CaFeO4 was characterized using XRD, FT-IR, UV–Vis, TEM, SEM, Raman, and redox titration. FT-IR analysis confirmed the presence of the Fe–O stretching vibrations in all the freeze-dried CaFeO4 powders, signifying the successful preparation of the materials. The physicochemical characteristics of raw water, such as turbidity, color, COD, pH, EC, and TDS, were analyzed before and after treatment with CaFeO4. A jar test was performed to evaluate the reactivity and efficiency of the CaFeO4 toward wastewater treatment through coagulation/flocculation processes. After coagulation using CaFeO4, the pollutants levels were reduced COD (43.56–71.56%) and turbidity (97–99%), signifying the effectiveness of the as-prepared materials. CaFeO4 was successfully produced at various temperatures and was stable enough to be stored at room temperature for over six months without significantly decomposing.Graphical abstract

Acetone-Treated Au Nanoparticles Supported on CeO2 for the Wet Air Oxidation of Dimethylformamide

Acetone-Treated Au Nanoparticles Supported on CeO₂ for the Wet Air Oxidation of Dimethylformamide

Effective photo-catalytic degradation of Malachite Green with water stable Cu based aliphatic di-carboxylate MOFs

Four different mesoporous Cu-MOFs named as Cu(Pima), Cu(Suba), Cu(Azla) and Cu(Seba) were prepared from aliphatic di-carboxylate linkers with the dimeric Cu paddle wheels as Secondary Building Units (SBUs). These as-synthesized aliphatic Cu-MOFs were applied as fresh heterogeneous catalysts for the catalytic wet peroxide oxidation of simulated Malachite Green waste-water and characterized using PXRD, FT-IR, Fe-SEM and BET. The results exhibited a better catalytic degradation efficiency of Cu(Seba) and Cu(Azla) (>90% in 200 mins) as compared to Cu(Pima) and Cu(Suba). It was established that degradation efficiency of Cu(seba) was approximately 9.8 times better than the rest of the synthesized Cu(MOFs). It was recognized that increasing the organic linker length can evidently boost the dye degradation process. Under optimum conditions, the degradation efficiency of 98% and 97% for Cu(Seba) and Cu(Azla) were achieved respectively. A optimal condition of 1.0 mL H2O2, 50 °C temperature and 3.5 pH was obtained. A recyclability experiment of four runs was performed for Cu(Seba) and Cu(Azla) which exhibited they maintained an effective degradation efficiency of ∼80% simulated MG solution. These analytical results of the degradation efficiency for Cu(Seba) and Cu(Azla) led us on a conclusion that, as synthesized Cu-MOFs outperformed several other reported MOFs, nanoparticles, adsorbents etc., as heterogeneous catalysts in the field of dye degradation for wastewater treatment.

Microplastics Trophic Transfer in Seafood Varieties Caught from the Coastal Waters off Negombo

Microplastics are a pervasive global pollutant that poses risks to marine organisms including commercially important species and poses threats even to humans. However, the trophic transfer of microplastics is yet to be understood. The present study was to study the occurrence of microplastics in five species used as seafood and in zooplankton, representing different trophic levels and feeding habits caught within coastal waters off Negombo. The Negombo coastal environs are known for high ecological diversity still subjected to massive anthropogenic activities as a major fishing and tourism hub in Sri Lanka. The same area was subjected to contaminating microplastics after the MV X-Press Pearl ship disaster which caught fire and spilled the largest point source of microplastic nurdles pollution in the world. Field sampling was carried out from October to-December 2021 in Negombo, Sri Lanka. The study included zooplankton, some fish (Sardinella gibbosa (n=10), Hemiramphus archipelagicus (n=10), and Ephipphus orbis (n=10)), crustaceans (Scylla serrata, (n=10)) and a bivalve (Perna perna, (n=10)). The samples were subjected to wet peroxide oxidation and acid digestion. Microplastic identification was conducted microscopically and confirmed with Fourier-Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, and Nile red staining techniques. Microplastics were present in all the species studied except zooplankton samples. Four polymer types were identified and confirmed as Polyamide (PA), Polystyrene (PS), Polypropylene (PP), and Polycaprolactone (PCL). According to the literature, this is the first recorded PCL contamination in marine species in Sri Lanka. Fibers were the most abundant microplastic type recorded followed by fragments, films, spheres, and flakes. Red, green, blue, yellow, black, and transparent microplastics were recorded while blue colour was the most prominent. The mean number of microplastics recorded was 0.93±0.29 for S. gibbosa, 0.97±0.17 for H. archipelagicus, 0.53±0.09 for E. orbis, 0.36±0.16 for S. serrata and 1.13±0.29 items/g for P. perna. Investigation of microplastic concentrations at different trophic levels suggests that organisms at lower trophic levels are at greater risk of microplastics. 
 Keywords: Microplastics, Trophic transfer, Marine organisms, Seafood, Negombo

Solvent screening for the extraction of aromatic aldehydes

The aromatic aldehydes vanillin, syringaldehyde, and p-hydroxybenzaldehyde find applicability in a broad field ranging from additives in food, cosmetics, and fragrances to precursors of electrochemically active substances used in organic redox flow batteries. These aldehydes can be obtained by wet oxidation of lignin a macromolecule present in woody biomass followed by the isolation via solvent extraction from the resulting acidic solutions.The present study investigates solvents grouped by esters, ethers, terpenes, and terpenoids, in addition to 1-octanol for their performance in extraction of the aromatic aldehydes vanillin, p-hydroxybenzaldehyde and syringaldehyde from an acidic aqueous solution. Solvent extractions are performed at 25 and 50 °C in double-walled tempered separation funnels. The overall extraction efficiency is determined by back-extractions performing a pH-swing at 25 °C. Aldehyde concentrations are measured by HPLC-UV. Karl-Fischer titration and total organic carbon measurements are used to account for the mutual solubility.The best-performing solvent in the case of aldehyde yields at low mutual solubility is given by the ester butyl acetate with extraction efficiencies of 96.53 % for p-hydroxybenzaldehyde, and > 95 % and > 93 % for vanillin and syringaldehyde, respectively. The highest overall extraction efficiency among all solvents suitable for alkaline back-extraction is achieved by cyclopentyl methyl ether with 94.73 % for p-hydroxybenzaldehyde, 94.04 % for vanillin and 87.91 % for syringaldehyde. The solvents geraniol, 1-octanol, ethyl acetate, and 2-methyl tetrahydrofuran show increased uptake of water with ethyl acetate, and 2-methyl tetrahydrofuran pointing out a high solvent loss with 9.82 vol% and 15.84 vol%, respectively. The terpene p-cymene showed preferable extraction of vanillin and syringaldehyde over p-hydroxybenzaldehyde with mutual solubility below 0.02 vol%, which makes it and interesting candidate for multistage solvent extraction.

Development and Fabrication of MOSFET-Based Radiation Dosimeter (RadFET) for Enhanced Performance in Space Missions

This work presents the development and fabrication process of a radiation dosimeter based on Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) technology, known as RadFET. The aim of this study is to determine the specifications of the RadFET sensor for use in space missions by the Egyptian Space Agency in SPNeX mission. We have successfully determined the sensor specifications, specified the required electronic components for readout circuits, and confirmed the correct operation of the RadFET device through device simulations and radiation-induced damage models. The fabrication process was conducted at Zewail City of Science, Technology and Innovation cleanroom facility, utilizing Sentaurus TCAD for device and process simulations. We have conducted fabrication experiments for phosphorus spin-on dopant application, dry oxide growth, and wet oxidation using water vapor bubblers. The dosimeter readout PCB fabrication and assembly phases have been successfully completed. The developed RadFET dosimeter holds great promise for radiation monitoring in space missions, ensuring enhanced safety and reliability of electronic systems.

Implantable pH Sensing System Using Vertically Stacked Silicon Nanowire Arrays and Body Channel Communication for Gastroesophageal Reflux Monitoring.

Silicon nanowires (SiNWs) are emerging as versatile components in the fabrication of sensors for implantable medical devices because of their exceptional electrical, optical, and mechanical properties. This paper presents a novel top-down fabrication method for vertically stacked SiNWs, eliminating the need for wet oxidation, wet etching, and nanolithography. The integration of these SiNWs into body channel communication (BCC) circuits was also explored. The fabricated SiNWs were confirmed to be capable of forming arrays with multiple layers and rows. The SiNW-based pH sensors demonstrated a robust response to pH changes, and when tested with BCC circuits, they showed that it was possible to quantize based on pH when transmitting data through the human body. This study successfully developed a novel method for SiNW fabrication and integration into BCC circuits, which could lead to improvements in the reliability and efficiency of implantable medical sensors. The findings demonstrate significant potential for bioelectronic applications and real-time biochemical monitoring.

G‐C3N4 Coating Enhanced Cu@AC for Catalytic Wet Air Oxidation of Phenol under Mild Conditions

AbstractA Cu‐based supported catalyst with g‐C3N4 coating (Cu/g‐C3N4@AC) was prepared by facile in‐situ growth over activated carbon surface with urea and Cu(NO3)2, and the catalytic performance for wet air oxidation of phenolic wastewater was investigated. The effects of different reaction conditions (catalyst, temperature, pressure and pH) were examined. The results show that under the catalysis of Cu/g‐C3N4@AC phenol could be completely oxidized at 120 °C and 0.5 MPa O2 with COD removal of 92.6 % (from 4883 mg/L to 361 mg/L). TEM, BET, XRD, FTIR and XPS characterizations showed that g‐C3N4 coating could strengthen the metal surface interaction via the Cu−N−C bonds formation, thus suppressing the aggregation of the active components on the surface and mitigating the catalyst deactivation. Moreover, the interaction between the Cu species and the g‐C3N4 structure facilitates the electron transfer and thus significantly boost up the catalytic activity. These findings help explore efficient catalysts for the wastewater treatment via wet air oxidation under mild conditions.

Degradation of the cytostatic drug bicalutamide by photo-assisted catalytic wet peroxide oxidation

The presence of cytostatic drugs, such as bicalutamide (BICA), in aquatic compartments reveals the necessity of developing efficient processes for their elimination in wastewater treatment plants (WWTP). This work explores for the first time the use of natural magnetite as a low-cost catalyst in the photo assisted — catalytic wet peroxide oxidation (UV-CWPO) of BICA. For this purpose, real WWTP secondary effluents were spiked with 100 μg/L BICA and subjected to UV-CWPO. Preliminary runs comparing UV photolysis, UV/H2O2, CWPO and UV-CWPO confirmed the synergistic effect of UV radiation and the CWPO process employing magnetite. Afterwards, a parametric study was performed evaluating the influence of the pH, catalyst load, H2O2 dosage, temperature and water matrix. Under optimum operating conditions (pH 0: 6, [magnetite]: 375 mg/L and [H2O2]: 75 mg/L), 99.7 % BICA degradation and 60.7 % mineralization were reached after 30 min in WWTP effluent. UV-CWPO also proved to be effective in hospital wastewater. Catalyst activity was studied in 5 consecutive runs, showing great stability for both BICA removal and TOC elimination. Finally, phytotoxicity tests revealed a lower toxicity in the UV-CWPO effluent compared to the untreated stream. Hence, UV-CWPO proved to be a feasible to eliminate risky cytostatic drugs in relevant environmental matrices.

Optimasi Konsentrasi Fe(II) pada Metode Wet Peroxide Oxidation (WPO) untuk Identifikasi Mikroplastik Polypropylene (PP)

One of the global problem is plastic waste, if not handled properly it will cause waterpollution. Plastic will degrade into samall pasrticles called microplastic. Polyperopylene plastic will be cut very small size and soaked in water and left in an open room for one month, so that the microplastic degrade naturally and become contaminated by organic impurities. The method used is Wet Peroxide Oxidation (WPO) which was adapted from the National Oceanic and atsmospheric (NOAA). Optimization was carried out the concentration of the Fe(II) catalyst with variations (0.025, 0.05, 0.075, 0.1, 0.125) M. The research result showed that the optimum condition for the Fe(II) consentration was 0.1 M as evidenced by the microplastic mass obtained. Characterization tests were carried out using a stereo microscope, and microplastics were found in the form of fragments and filament.

Odour reduction of kraft lignin by wet oxidation

This study assesses wet oxidation of partially concentrated Kraft black liquor (40% dry matter) as a method for odour reduction of the lignin obtained from it by acid precipitation. To this end, and for the first time ever, the effects of wet oxidation temperature (120–150 ºC) and pressure (10–50 bar) on the odour profile of both the black liquor and the acid precipitated lignin were analysed. 2-methoxyphenol, dimethyl disulphide and dimethyl trisulphide were the main responsible compounds of the black liquor odour and, in the case of the precipitated lignin, aldehydes and organic acids also contributed. The most odourless lignin was the one precipitated from Kraft black liquor oxidised at the most severe conditions tested (150 °C and 50 bar for 2 h). However, these also caused a reduction in the lignin yield, as well as significant compositional and appearance changes, thus limiting its use in certain fields.

Structuring Interdigitated Back Contact Solar Cells Using the Enhanced Oxidation Characteristics Under Laser‐Doped Back Surface Field Regions

Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer‐based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser‐doped n++ back surface field (BSF) regions with high‐phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl3 diffusion serve as a precursor layer for the formation of local heavily laser‐doped n++ BSF regions. The laser‐doped n++ BSF regions exhibit a 2.6‐fold increase in oxide thickness compared to the nonlaser‐doped n+ BSF regions after undergoing high‐temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof‐of‐concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%.