Oxidation Method Research Articles

Engineering the defect distribution via boron doping in amorphous TiO2 for robust photocatalytic NO removal

Nitric oxide (NO) pollutant can threaten the regional environment and human health. Solar-powered photocatalytic oxidation method is desirable for NO removal (ppb level) at ambient conditions, but suffers from the unsatisfactory activity and poor selectivity due to the sluggish molecular oxygen activation. Herein, we demonstrate that efficient photocatalytic NO removal can be realized by modulating the defects distribution of amorphous TiO2 via boron doping. Theoretical calculations and experimental results reveal that H3BO3 modification can refine the structure of surface oxygen vacancies, promoting electron-rich molecular oxygen activation to •OH. Meanwhile, bulk-phase oxygen defects can be filled by free-state B atoms, accelerating the electron transfer via Ti-O-B bonding. Homogeneous boron-doped amorphous TiO2 achieves about 5 times higher NO removal efficiency (∼50%) than that of amorphous TiO2 (∼9%) without releasing remarkable NO2 (selectivity, ∼97%). This study provides a state-of-the-art approach for robust photocatalytic NO removal by engineering the defect distribution.

Etching-free pixel definition in InGaN green micro-LEDs

The traditional plasma etching process for defining micro-LED pixels could lead to significant sidewall damage. Defects near sidewall regions act as non-radiative recombination centers and paths for current leakage, significantly deteriorating device performance. In this study, we demonstrated a novel selective thermal oxidation (STO) method that allowed pixel definition without undergoing plasma damage and subsequent dielectric passivation. Thermal annealing in ambient air oxidized and reshaped the LED structure, such as p-layers and InGaN/GaN multiple quantum wells. Simultaneously, the pixel areas beneath the pre-deposited SiO2 layer were selectively and effectively protected. It was demonstrated that prolonged thermal annealing time enhanced the insulating properties of the oxide, significantly reducing LED leakage current. Furthermore, applying a thicker SiO2 protective layer minimized device resistance and boosted device efficiency effectively. Utilizing the STO method, InGaN green micro-LED arrays with 50-, 30-, and 10-µm pixel sizes were manufactured and characterized. The results indicated that after 4 h of air annealing and with a 3.5-μm SiO2 protective layer, the 10-µm pixel array exhibited leakage currents density 1.2 × 10−6 A/cm2 at −10 V voltage and a peak on-wafer external quantum efficiency of ~6.48%. This work suggests that the STO method could become an effective approach for future micro-LED manufacturing to mitigate adverse LED efficiency size effects due to the plasma etching and improve device efficiency. Micro-LEDs fabricated through the STO method can be applied to micro-displays, visible light communication, and optical interconnect-based memories. Almost planar pixel geometry will provide more possibilities for the monolithic integration of driving circuits with micro-LEDs. Moreover, the STO method is not limited to micro-LED fabrication and can be extended to design other III-nitride devices, such as photodetectors, laser diodes, high-electron-mobility transistors, and Schottky barrier diodes.

Treatment of pistachio processing industry wastewaters by supercritical water oxidation in a continuous-flow reactor

ABSTRACT The objective of the present study is the treatment of pistachio processing industry wastewaters (PPIW) using the supercritical water oxidation method. The experiments were conducted within a 400–600°C temperature range and a 30–150 s reaction time range, while maintaining a constant pressure of 25 MPa and using an O2/COD ratio of 1:1. To observe the effects of the initial PPIW and O2 concentrations on the treatment efficiency, experiments were also conducted with O2/COD ratios ranging from 0.5 to 3, while maintaining a constant reaction temperature and time of 500°C and 60 s, respectively. The influence of reaction temperature, reaction time and O2/COD ratio on the total organic carbon (TOC) and total nitrogen (TN) contents of the liquid PPIW effluents were investigated. Treatment efficiencies up to 99.75% regarding TOC conversion and 78.72% regarding TN conversion were obtained in very short reaction times. Additionally, the kinetics of oxidation of PPIW was studied, and reaction rate expressions based on TOC and TN were proposed.

Metabolic availability of amino acids in humans.

Knowledge of amino acid bioavailability and the effect of combining complementary protein sources are required to determine how to best meet an individual's protein and indispensable amino acid needs. Traditionally, protein quality of foods has been assessed using digestibility data. Digestibility may overestimate bioavailability of some amino acids particularly those more susceptible to heat and processing. The indicator amino acid oxidation (IAAO) method has been validated and applied to determine amino acid bioavailability termed metabolic availability of the first limiting amino acid of a proteinaceous food. The metabolic availability of the limiting amino acid in the test protein is determined as a ratio of the indicator amino acid oxidation response to graded intakes of the test protein compared to the indicator response to a reference protein (crystalline amino acid patterned after egg protein). The IAAO method has also been applied to assess the effect of protein complementation directly in humans on the overall protein quality of the diet. The results demonstrate that protein complementation augments the limiting amino acid supply and increases protein synthesis.

Synergistic modulation of the d-band center in Ni3S2 by selenium and iron for enhanced oxygen evolution reaction (OER) and urea oxidation reaction (UOR)

Efficient production of green hydrogen energy is crucial in addressing the energy crisis and environmental concerns. The oxygen evolution reaction (OER) poses a challenge in conventional overall water electrolysis due to its slow thermodynamically process. Urea oxidation reaction (UOR) offers an alternative anodic oxidation method that is highly efficient and cost-effective, with favorable thermodynamics and sustainability. Recently, there has been limited research on bifunctional catalysts that exhibit excellent activity for both OER and UOR reactions. In this study, we developed a selenium and iron co-doped nickel sulfide (SeFe-Ni3S2) catalyst that demonstrated excellent Tafel slopes of 53.9 mV dec−1 and 16.4 mV dec−1 for OER and UOR, respectively. Density Functional Theory (DFT) calculations revealed that the introduction of metal (iron) and nonmetallic elements (selenium) was found to coordinate the d-band center, resulting in improved adsorption/desorption energies of the catalysts and reduced the overpotentials and limiting potentials for OER and UOR, respectively. This activity enhancement can be attributed to the altered electronic coordination structure after the introduction of selenium (Se) and iron (Fe), leading to an increase in the intrinsic activity of the catalyst. This work offers a new strategy for bifunctional catalysts for OER and UOR, presenting new possibilities for the future development of hydrogen production and novel energy conversion technologies. It contributes towards the urgent search for technologies that efficiently produce green hydrogen energy, providing potential solutions to mitigate the energy crisis and protect the environment.

Efficient incorporation of highly migratory thallium into struvite structure: Unraveling the stabilization mechanisms from a mineralogical perspective

The remediation of high-concentration thallium (Tl+) contaminated wastewater is a critical environmental concern. Current research emphasizes the effectiveness of adsorption and oxidation methods for Tl+ treatment, yet challenges persist in enhancing their performance. This study explores the feasibility of emergency Tl+ wastewater treatment and elucidates the mechanisms of Tl+ incorporation into mineral structures, with a focus on the struvite mineral as a framework for Tl+ integration via NH4+ ion exchange. To assess the efficacy and mechanisms of Tl+ immobilization, we utilized comprehensive analytical techniques, including X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Thermogravimetric Analysis (TG), and Density Functional Theory (DFT) calculations. The findings reveal that struvite adsorbs Tl+ onto its surface, followed by an ion exchange process between monovalent cations (NH4+/K+) within the structure and Tl+. Ultimately, Tl+ is incorporated in the form of a (NH4,Tl)MgPO4 solid solution within the structure, achieving a remarkable maximum incorporation capacity of 320.56 mg/g, which significantly surpasses the capacity of typical adsorbents. The findings demonstrate significant Tl+ incorporation, validating the approach for emergency wastewater treatment and suggesting the potential of mineralogy in environmental remediation. This research contributes to advancing heavy metal wastewater treatment strategies, offering a foundation for further investigation.

Synthesis of zinc doped nickel cobaltite nanoparticles through homogeneous precipitation method for catalytic oxidation of styrene

The present study reports homogeneous precipitation method for the preparation of Zn2+ substituted Ni-Co LDH precursors and their subsequent conversion to Ni1−xZnxCo2O4 nanoparticles (NPs) via calcination. Different analytical techniques were used for characterization of the precursors and the Ni1−xZnxCo2O4 NPs. After characterization, catalytic activity of the Ni1−xZnxCo2O4 NPs was investigated towards oxidation of styrene. The effect of reaction time and amount of catalyst on the oxidation of styrene was also investigated. The Ni1−xZnxCo2O4 NPs exhibit better performance as catalyst for the styrene oxidation compared to undoped NiCo2O4 NPs.

Effects of promoter and dedoping process on electrorheological response of polyaniline-graft-chitosan copolymer

In this study, electrorheological (ER) properties of biodegradable and conducting polyaniline-graft-chitosan (PAni-g-CS) copolymer particles were investigated. For this purpose, PAni and PAni-g-CS particles were synthesized by using in situ oxidative radicalic polymerization method. At first, PAni and PAni-g-CS/silicone oil (SO) ER suspensions (15% V/V) were subjected to external electric field and they exhibited low ER activity. When the external electric field strengths ([Formula: see text] were increased, both the suspensions showed electrical breakdown. Therefore, virgin PAni and PAni-g-CS were first subjected to dedoping process by treating with 1.0 M NaOH(aq) and non-ionic surfactant Triton X-100 (T-X) surfactant to enhance the expected ER activity and prevent the electrical breakdown. But we observed that the addition of T-X as promoter had no significant effect on the ER activity. On the other hand, electric filed-induced viscosities of both the suspensions were observed to enhance after the dedoping (DD) process and electrical breakdown prohibited. After the DD process, DD PAni-g-CS/SO ER system exhibited the highest electric field-induced viscosity by reaching 400[Formula: see text]Pa[Formula: see text]⋅[Formula: see text]s at [Formula: see text][Formula: see text]kV/mm. The highest ER efficiency was also obtained for DD PAni-g-CS/SO system at 15% (V/V) as 79. Additionally, typical shear thinning non-Newtonian viscoelastic behavior was observed under externally applied E. The conduction model of DD PAni-g-CS/SO system was determined to well fit the conduction model by showing a slope of [Formula: see text] calculated from the E vb. yield stress graph. In conclusion, conducting and biodegradable-dedoped PAni-g-CS particles would be a good candidate for potential ER applications as dry-based ER materials having high colloidal stability of 76%.

Composites of Zn-Co spinel ferrites and PANI: Structural, magnetic, microwave absorption characterization in 18–40 GHz

The present research work deals with the fabrication of composites containing spinel ferrites and polyaniline as high-performance microwave absorbers. The composites were prepared by the inter-mixing of Zn-Co spinel ferrites and PANI polymer in a 4:1 M ratio using the mechanical blending technique. The sol–gel citrate route was employed to synthesize Zn-Co spinel ferrites, while the oxidative polymerization method was used to synthesize PANI. The structural, morphological, magnetic, and microwave absorption properties of the composite samples were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA), respectively. The X-ray diffraction patterns indicated the crystalline nature of spinel ferrites and the amorphous nature of PANI. The magnetic properties revealed that saturation magnetization (Ms) increased significantly with the addition of spinel ferrites into PANI owing to its magnetic nature. The microwave absorption results showed that the minimum reflection loss (RL) reached up to −26.63 dB at 20.72 GHz with the effective bandwidth of 5.95 GHz in the K-band and −39.16 dB at 35.68 GHz with the effective bandwidth of 8.1 GHz in the Ka-band for composition NZP. This study indicated that the prepared SF/PANI composites can be proposed as a promising absorbent in the K-band and Ka-band.

Remarkable fluorescence enhancement of acridine orange and rhodamine B through immobilization on zirconia nanotube array film and its application on nitrite sensing

Zirconia nanotube array films (ZNAF) prepared by anodic oxidation method were used as immobilization materials for acridine orange (AO), rhodamine B (RB) and AO-RB systems. A comparative study on their fluorescence emission intensity, fluorescence resonance energy transfer (FRET) and fluorescence detection of nitrite in aqueous solutions and on immobilization films with ZNAF as carriers was carried out. Results demonstrate that the solution pH values and immobilization on ZNAF have a great influence on the performance of these fluorescent molecules. Compared with aqueous solutions, the fluorescence emission intensity of AO and RB is considerably increased by immobilization, which is 8.0 and 4.2 times higher than the original, respectively. The energy transfer efficiency (E) of the AO-RB system increases from 40.9 % to 84.8 % by loading it on ZNAF. Moreover, after immobilization onto ZNAF, the fluorescence detection performance of nitrite is also significantly improved. The limit of detection decreases from 0.95 ng/mL to 0.22 ng/mL and the sensitivity increases from 939.18 to 15,031.68 mL/μg through loading AO onto ZNAF.

Effects of Chlorogenic Acid on Lowering IgE-Binding Capacity of Soybean 7S: Comparison between Covalent and Noncovalent Interaction.

Allergenicity of soybean 7S protein (7S) troubles many people around the world. However, many processing methods for lowering allergenicity is invalid. Interaction of 7S with phenolic acids, such as chlorogenic acid (CHA), to structurally modify 7S may lower the allergenicity. Hence, the effects of covalent (C-I, periodate oxidation method) and noncovalent interactions (NC-I) of 7S with CHA in different concentrations (0.3, 0.5, and 1.0 mM) on lowering 7S allergenicity were investigated in this study. The results demonstrated that C-I led to higher binding efficiency (C-0.3:28.51 ± 2.13%) than NC-I (N-0.3:22.66 ± 1.75%). The C-I decreased the α-helix content (C-1:21.06%), while the NC-I increased the random coil content (N-1:24.39%). The covalent 7S-CHA complexes of different concentrations had lower IgE binding capacity (C-0.3:37.38 ± 0.61; C-0.5:34.89 ± 0.80; C-1:35.69 ± 0.61%) compared with that of natural 7S (100%), while the noncovalent 7S-CHA complexes showed concentration-dependent inhibition of IgE binding capacity (N-0.3:57.89 ± 1.23; N-0.5:46.91 ± 1.57; N-1:40.79 ± 0.22%). Both interactions produced binding to known linear epitopes. This study provides the theoretical basis for the CHA application in soybean products to lower soybean allergenicity.

Process Optimization and Kinetic Modeling for Sucrose Acylation to Sucrose-6-acetate through the Dibutyltin Oxide Method

Process Optimization and Kinetic Modeling for Sucrose Acylation to Sucrose-6-acetate through the Dibutyltin Oxide Method

Dietary Lysine Requirements of Older Adults Stratified by Age and Sex

BackgroundCurrent recommendation for lysine in older adults, 30 mg/kg/d, is based on young adult data. Evidence suggests that amino acid requirements may differ between young and old adults with both sex and age having an effect in the elderly. ObjectivesThis study aimed to define the lysine requirements in healthy older adults using the indicator amino acid oxidation (IAAO) method with L-[1-13C] phenylalanine as the indicator and to compare the derived estimates based on age: 60–69 y and >70 y. MethodsFourteen healthy males and 16 healthy females [>60 y, body mass index (BMI) = 26.3 kg/m2] were randomly assigned to receive 3–7 lysine intakes from 10 to 80 mg/kg/d. Subjects were adapted to a standard liquid diet providing 1.0 g/kg/d protein and adequate energy, for 2 d, with indicator oxidation measurements performed on day 3. The rate of release of 13CO2 from the oxidation of L-[1-13C] phenylalanine was measured in breath. A 2-phase linear mixed-effect model, and parametric bootstrap were used to determine mean lysine requirements and the 95% confidence intervals (CIs). The overlap of the 95% CI between the 2 age groups were used to compare the requirement estimates. The null hypothesis was accepted if the interval contained zero. ResultsThe mean and upper 95% CI of the lysine requirement for females were 32.9 and 40.9 and 46.2 and 53.7 mg/kg/d for those aged 60–69 y and >70 y, respectively. The mean and upper 95% CI of the lysine requirement for the 2 groups of males were not different so was combined to yield a mean and 95% CI of 32.2 and 38.2 mg/kg/d. ConclusionsTo our knowledge, this is the first study to report on the lysine requirement in adults aged >60 y. These results provide a basis from which the adequacy of diets to meet lysine needs of older adults can be assessed.The trial was registered at clinicaltrials.gov as NCT02008955 (https://clinicaltrials.gov/study/NCT02008955).

Recent Advances in Manganese(III)-Assisted Radical Cyclization for the Synthesis of Natural Products: A Comprehensive Review.

Natural products play an important part in synthetic chemistry since they have many pharmacological properties and are used as active drug compounds in pharmaceutical chemistry. However, synthesis of these complex molecules is difficult due to the requirement of various synthetic steps, which include highly regio- and stereoselectivity. Therefore, oxidative radical cyclization assisted by manganese(III) acetate serves as an important step in obtaining spiro-, tricyclic, tetracyclic, and polycyclic derivatives of these compounds. Manganese(III)-based reactions offer a single-step regio- and stereoselective cyclizations and α-acetoxidations, reducing the number of synthetic steps. Also, the manganese(III)-mediated oxidative free radical cyclization method has been successfully applied for the synthesis of cyclic structures found in many natural products. This article presents a broad overview of manganese(III)-based radical reactions of natural products as a key step in overall synthesis. The authors have classified natural product synthesis processes assisted by manganese(III) acetate as intermolecular, intramolecular, oxidation, acetoxidation, aromatization, and polymerization reactions, respectively.

Coupled one-pot oxidative extractive desulfurization of a model fuel catalyzed by nanostructured-ZIF-67/Biomass-derived activated carbon composite

The simultaneous oxidation and extraction of refractory sulfur compounds, such as DBT, has emerged as one of the most efficient complementary procedures for the HDS process in achieving ultradeep desulfurization of fuels. In this paper, a bio-based activated carbon (AC) obtained from the waste of date palm bark has been utilized as an abundant, green, and low-cost support for synthesizing a stable metal-organic framework, zeolitic imidazolate framework-67 (ZIF-67), on its structure to reach a novel nanocomposite catalyst (AC/ZIF-67) for the removal of DBT from a model fuel through the extractive oxidative desulfurization method. The accuracy of the AC/ZIF-67 catalyst formation was comprehensively characterized using XRD, FTIR, FESEM, BET, and TGA analytical techniques. Subsequently, the newly synthesized nanocomposite catalyst was employed efficiently for removing DBT from a toluene solution, acting as a model fuel. The impact of various operating variables, i.e. catalyst dosage, the temperature of reaction, oxidant-to-sulfur (O/S) molar ratio, contact time, initial concentration of DBT, and volume of extraction solvent on the removal efficiency has been thoroughly investigated. The results revealed that employing only 25 mg of the AC/ZIF-67 catalyst could achieve a remarkably high efficiency of around 98 % after one hour oxidation of a 25 ppm DBT solution in the presence of TBHP, followed by extraction using acetonitrile. This was achieved while maintaining a constant temperature of 60 °C and an O/S ratio of 20. The obtained results confirm the potential application of ACs for supporting MOF catalysts in various catalytic processes such as desulfurization.

Improvement of water resistance in printed carbon electrode mixing cellulose nanofiber

Carbon electrodes are widely used for battery and electrolysis due to wide potential window and chemical stability. The carbon electrode made from carbon material ink using printing process is expected as electrode with low cost and large area. Therefore, we have developed carbon material inks and printed electrode by combining micro-wave treated graphite oxide (MwGO) and screen-printing method. However, the MwGO electrodes exhibited low water resistance. Cellulose nanofiber is mixed into the MwGO ink to improve water resistivity. As a result, increase in water resistance is achieved with maintaining electrical conductivity.

Effects of Different Oxidation Methods on the Wetting and Diffusion Characteristics of a High-Alumina Glass Sealant on 304 Stainless Steel.

Glass-to-metal seals are a very important element in the construction of vacuum tubes, electric discharge tubes, pressure-tight glass windows in metal cases, and metal or ceramic packages of electronic components. This paper presents the influence of different pretreatment methods on the high-temperature wettability of 304 stainless steel by high-alumina glass sealing. The pretreatment of the steel included laser surface melting and pre-oxidizing. The bonding characteristics of glass and stainless steel directly depend on the wettability in terms of the measured wetting angle, the type of oxide formed at the stainless steel surface, and the microstructural changes during the manufacturing process. The oxide film thickness on the stainless steel surface was evaluated to determine the optimal parameters. The film was wetted with high-alumina glass powder at different temperatures. The results showed that pre-oxidation decreased the wetting angle from 56.2° to 33.6°, while for the laser-melted surface, the wetting angle decreased from 49.8° to 31.5°. Scanning electron microscopy (SEM) revealed that the oxide film on the laser-melted surface was thicker and denser than that formed on the pre-oxidized surface. The present work shows that laser surface melting has a greater beneficial influence on the wetting and diffusion characteristics of 304 stainless steel sealed by high-alumina glass.

Removal and detoxification of iprodione in water using didodecyldimethylammonium bromide-montmorillonite organoclay and manganese dioxide.

Combination of organoclay sorption with manganese(IV) oxide (MnO2) catalyzed catechol oxidation was studied for the removal of a dicarboximide fungicide, iprodione, from water. Iprodion in water was sorbed on didodecyldimethylammonium bromide (DDAB)-modified montmorillonite (MT) organoclay and converted into the degraded product, 3,5-dichloroaniline (DCA). The degree of sorption increased by the modification with DDAB, because of the formation of a hydrophobic region for the incorporation of iprodione and negligibly interfered by coexisting MnO2. The half-life for the degradation of irodione in water at 25°C was 7 days, whreas it reduced to 15min in the organoclay. The activation energy, 65.4 ± 4.8kJmol-1, for the first-order reaction in the aqueous solution (pH 7.0) decreased to 43.9 ± 1.8kJmol-1 in the organoclay, indicating the catalytic activity of the organoclay that accelerates the hydrolysis reaction of iprodione. In the coexistence of appropriate amounts of MnO2 and catechol, the degraded product, DCA, reacted with oxidized products of catechol to form a water-insoluble precipitate and was successfully eliminated from water. The results obtained in the present study strongly suggest the applicability of the combined method of organoclay sorption method and MnO2-catalyzed oxidation for the diffusion control of toxic agrochemicals.

A New Strategy for the Treatment of Old Corrugated Container Pulping Wastewater by the Ozone-Catalyzed Polyurethane Sponge Biodegradation Process.

Old Corrugated Container (OCC) pulping wastewater has a complex organic composition and high levels of biotoxicity. The presence of dissolved and colloidal substances (DCSs) is a major limiting factor for pulp and paper companies to achieve closed-water recycling. In order to solve this problem, the coupled ozone-catalyzed oxidation and biodegradation (OCB) method was used to treat OCC pulping wastewater in this study. A polyurethane sponge was used as the basic skeleton, loaded with nano TiO2 and microorganisms, respectively, and then put into a reactor. After an 8-min ozone-catalyzed oxidation reaction, a 10-h biological reaction was carried out. The process was effective in removing organic pollutants such as COD and BOD5 from OCC paper whitewater. The removal rates of COD and BOD5 were 81.5% and 85.1%, respectively. By using the polyurethane sponge to construct a microenvironment suitable for microbial growth and metabolism, this study successfully applied and optimized engineered bacteria-white rut fungi (WRF)-in the system to achieve practical degradation of OCC pulping wastewater. Meanwhile, the biocompatibility of different microbial communities on the polyurethane sponge was analyzed by examining the degradation performance of OCC pulping wastewater. The structure of microbial communities loaded on the polyurethane sponge was analyzed to understand the degradation mechanism and microbial reaction behavior. White-rot fungi (Phanerochaete) contributed more to the degradation of OCC wastewater, and new strains adapted to OCC wastewater degradation were generated.

Studi perbandingan metode oksidasi enzimatis terhadap aktivitas antioksidan ekstrak air teh kratom (Mitragyna speciosa Korth.)

One of the kratom (Mitragyna speciosa Korth.) products in Kapuas Hulu is fermented kratom tea powder, produced by the enzymatic oxidation process, which is very different from the processing of black tea. Until now, there has been no research on the manufacture of fermented kratom tea powder using the black tea enzymatic oxidation method. This study aimed to determine the differences between the enzymatic oxidation method to the antioxidant activity of water extract kratom tea. The technique used in this study was a comparative method to compare the data obtained from water extract kratom tea. The treatments compared were the manufacture of fermented kratom tea powder with the enzymatic oxidation method of the Kapuas Hulu community and the enzymatic oxidation method of black tea. The parameters tested in this study consisted of phenol content, flavonoid content, alkaloid content, and antioxidant activity. The study showed that the phenol and alkaloid contents were higher in product of black tea methods (199.22 mg GAE/g and 44.73%) than Kapuas Hulu traditional methods (50.45 mg GAE/g and 40.68%). Flavonoid content was higher in Kapuas Hulu traditional methods (169.32 mg QE/g) than black tea methods (48.77 mg QE/g). The difference was found in the antioxidant activity of the water extract kratom tea produced by two different enzymatic oxidation methods. The enzymatic oxidation of the black tea method was found to higher antioxidant activity of water extract kratom tea.