Values Of Reaction Rate Constants Research Articles

In-situ synthesis of sunlight-driven CuO-ZnO heterostructure photocatalyst for enhanced elimination of organic pollutants and CO2 reduction.

Removing hazardous organic pollutants, such as 4-nitrophenol (4-NP) and Congo red (CR) dyes from aqueous media and CO2 from the atmospheric medium remains a significant challenge. Herein, we report a facile in-situ synthetic approach for fabricating CuO-ZnO heterostructure photocatalysts through the surfactant-assisted co-precipitation method. The catalytic results demonstrate that the Cu1O-ZnO photocatalyst exhibits excellent activity under direct sunlight irradiation, owing to the heterostructure formation between the CuO and ZnO. The Cu1O-ZnO photocatalyst showed higher reaction rate constant (k) values of 0.20 min-1 for 4-NP and 0.09 min-1 for CR compared to previous reports. Additionally, efficient CO2 reduction was also achieved over Cu1O-ZnO photocatalyst. The optical and structural characterization results indicate that the improved photocatalytic reduction and degradation observed for the Cu1O-ZnO photocatalyst can be attributed to the strong synergistic interaction between p-type CuO and n-type ZnO and the construction of the p-n heterojunction. As a result, the absorption of visible light distinctly increased and inhibited the recombination rate of the photo-created electron-hole (e-/h+). Furthermore, the Cu1O-ZnO photocatalyst exhibited remarkable durability and recyclability, retaining high photoactivity (≥ 93%) after five cycles, demonstrating its potential for real-world applications in the photocatalytic reduction and degradation reactions under direct sunlight irradiation.

Comparative Study on Removal of Acid Violet 90 dye by using Catalytic Ozonation Processes with n.CeO2, n.ZnO and n.CeO2/n.ZnO Nanocatalysts and Kinetic Examination

The textile industry uses high amounts of water and dyestuffs, and accordingly, wastewater containing significant amounts of dyestuffs is produced, which have to be treated before being discharged to the environment. The aim of this study is the treatment of synthetic wastewater containing 50 mg/L Acid Violet 90 dyestuff with catalytic ozonation process have been investigated by using n.CeO2, n.ZnO and n.CeO2/n.ZnO (1:1, m:m) nanocatalysts. The process optimization has been performed with the pH, ozone dose, catalyst dose and reaction time parameters. While the optimum conditions have been determined as pH 3, 600 mg/L ozone dose, 10 min reaction time, for all three catalysts, catalyst doses have differed as 50 mg/L for n. CeO2, 30 mg/L for n.ZnO and n.CeO2/n.ZnO. The removal efficiencies of AV 90 have been achieved as 97.04, 96.2 and 95.7% for n.CeO2, n.ZnO and n.CeO2/n.ZnO catalysts, respectively. Kinetic analyses showed that color removal of AV 90 dyestuff followed First order kinetics with R2 values of 0.9987 (n.CeO2), 0.9912 (n.ZnO) and 0.9923 (n.CeO2/n.ZnO) and reaction rate constant values have been calculated as 0,3435 (n.CeO2), 0,3551(n.ZnO) and 0,3226 (n.CeO2/n.ZnO) min−1.

Cellulose acetate sheet supported gold nanoparticles for the catalytic reduction of toxic organic pollutants

Abstract Water contamination by toxic organic dyes represents a significant global challenge necessitating effective remediation strategies. Due to their high catalytic activity, considerable attention has been gained to metal-based nanocatalysts. Cellulose acetate sheets supported by gold nanoparticles through a reduction method were synthesized. The composite synthesized material presents a compelling platform for catalytic reduction in the remediation of toxic organic pollutants, ensuring controlled particle size and stability. In this study, the prepared cellulose acetate sheet (CAsheet) was dipped in a 0.001 M aqueous chloroauric acid (HAuCl4) solution and reduced by immersion in a 0.1 M sodium borohydride (NaBH4) aqueous solution. After the successful preparation of virgin cellulose acetate sheet (CAsheet) and gold-supported cellulose acetate sheet (Au-CAsheet) samples were assessed by scanning electron microscopy (SEM), X-ray crystallography (XRD), energy dispersive X-rays spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR) analysis. The catalytic reduction reaction of toxic compounds i.e. reduction of 4-nitroaniline (4-NA), Congo red (CR), and reactive yellow (RY-42) by using NaBH4. The catalytic activity of the Au-CAsheet was exhibited by the reaction rate constant (k app) values 0.3189, 0.1596, and 0.1593 min−1 for CR, 4-NA, and RY-42 respectively. This kind of procedure for Au-CAsheet synthesis may be valid for different applications in catalysis, sensing, and environmental application.

Flower-like hierarchical TS-1/Al2O3 composite supported NiMo catalysts for efficient hydrodesulfurization of dibenzothiophenes

Flower-like Al2O3 materials were successfully incorporated by TS-1 nanocrystals to synthesize Flower-like TS-1-Al2O3 (FTA) micro-mesoporous composite by a facile nano self-assembly method. FTA supported NiMo bimetallic catalysts (NiMo/FTA) were further constructed and applied to the hydrodesulfurization (HDS) reactions for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). FTA composites were constructed from flower-like pore structures stacked with nanosheets, which are conducive to the even load and dispersion of active species and the diffusion of macromolecular sulfur-containing compounds with relatively low resistance. The fabrication of TS-1 nanocrystals effectively enhanced the acidic sites, regulated the metal-support interaction, which could increase the stacking layer of MoS2 slabs, and producing more NiMoS-II type active phase. NiMo/FTA-10 presented the excellent HDS conversion of DBT (99.3 %) and 4,6-DMDBT (93.2 %) at 10 h−1, the highest reaction rate constant (2.6 × 10-7 mol g−1 s−1) and turnover frequency values (6.7 × 10-4 s−1) for 4,6-DMDBT HDS reaction. Compared to the direct desulfurization route (DDS), hydrogenation route (HYD) and isomerization route (ISO) can effectively eliminate the steric hindrance of 4,6-DMDBT, which is more conducive to the HDS reaction.

Oxygen-deficient WO3 for stable visible-light photocatalytic degradation of acetaldehyde within a wide humidity range

Indoor VOCs pollution has attracted broad attention for its harm to mankind’s health recent years. Photocatalytic degradation of indoor VOCs holds great prospects in addressing these health concerns in daily life. However, traditional photocatalysts have a large recombination rate of charge carriers and a decrease of the photocatalytic degradation efficiency under high relative humidity. Herein, uniform tungsten oxide nanoparticles with enriched oxygen vacancies (WO3-U) were synthesized by a direct annealing method with urea addition, which exhibited superior performance in the visible-light photocatalysis. The reaction rate constant value of photocatalytic acetaldehyde degradation over WO3-U catalyst was above 3 times higher than that of pristine WO3 sample. More importantly, the WO3-U catalyst maintained stable and excellent photocatalytic performance at relative humidity range of 25–100 %. Except for the enhanced photogenerated charges separation, abundant oxygen vacancies could effectively accelerate O2 activation to generate •O2−, which accounted mainly for the initial conversion of acetaldehyde. Then the subsequent transformation of •O2− into •OH to promoted the final mineralization of acetaldehyde. In addition, the presence of oxygen vacancies also facilitated H2O dissociation to form surface hydroxyl groups, which increased the adsorption of acetaldehyde, resulting in the consistent photocatalytic performance of WO3-U catalyst within a wide humidity range. This work provides guidelines to design visible-light responsive photocatalysts with efficient activity at high humidity conditions for indoor VOCs degradation.

Determination of the Kinetic Parameters of Thermal Degradation and Hydrodemetallization of a Mixture of the Heavy Fraction of Low-Temperature Coal Tar and Coal Shale

The laws of thermal degradation of the mixture of the heavy fraction of low-temperature coal tar and coal shale were investigated using dynamic thermogravimetry. The kinetic characteristics of the process were determined using various methods, including the Ozawa–Flynn-Wall, Friedman, non-parametric kinetics and Šesták–Berggren methods. It is shown that coal shale initiated changes in the kinetic parameters and decomposition rate of the heavy fraction of coal tar. It was found that a 13% content of coal shale in the mixture led to the maximum rate of weight loss of the heavy fraction of coal tar. A hydrodemetallization kinetic model of the mixture of the heavy fraction of low-temperature coal tar and coal shale is proposed. The kinetic parameters of the hydrodemetallization process were determined; in addition, the rate constants at various temperatures were estimated. The study shows that the distribution of trace elements in the hydrogenate from the initial mixture and in the hydrogenate from the solid residue was characterized by relatively low values of reaction rate constants. The maximum microelement distribution rate was achieved in the hydrogenate solid residue. Energy indicators of activation processes indicated that hydrodemetallization at low temperatures is advantageous from an energy point of view.

The Characteristics of Urease Enzyme of Green Bean Seeds (Vigna radiata L.) and Its Activity as An Antifungal Against Candida albicans

Urease is an enzyme responsible for catalyzing the hydrolysis reaction of urea into CO2 and NH3. The urease isolated in this study came from green bean seeds. The urease enzyme was then tested for its antifungal activity against Candida albicans. The research aims to extract and characterize the urease enzyme from green bean seeds and explore its potential use as an antifungal agent. Green bean seeds were smoothed with a mortar and pestle, followed by homogenization using a stirrer and cold centrifugation. The crude extract of the urease enzyme was assessed for its activity through the Nessler method and measured by employing a UV-Vis spectrophotometer at a wavelength of 500 nm. The well-diffusion method was conducted to determine the antifungal activity of rough enzyme extracts against C. albicans. Positive controls were 100% ketoconazole, and negative controls used a pH buffer of 7. The characterization of the urease enzyme from green bean seeds revealed the optimum urease activity at a concentration of 0.25 M, pH level of 7, and an incubation temperature of 35°C with a value of 32.115 U/mL. Maximum reaction rate (Vmax) and Michaelis-Menten constant value (KM) were obtained at 56.497 U/mL and 0.215 M, respectively. Antifungal tests of C. albicans resulted in strong inhibitory activity at a concentration of 100% crude urease extract of 12 mm inhibition zone. The inhibitory concentration value grows at least 0.5% by 0.25 mm and positive control of 19.802 mm.

Exfoliated MXene-AuNPs hybrid in sensing and multiple catalytic hydrogenation reactions.

The increasing use of nanomaterials in consumer products is expected to lead to environmental contamination sometime soon. As water pollution is a pressing issue that threatens human survival and impedes the promotion of human health, the search for adsorbents for removing newly identified contaminants from water has become a topic of intensive research. The challenges in the recyclability of contaminated water continue to campaign the development of highly reusable catalysts. Although exfoliated 2D MXene sheets have demonstrated the capability towards water purification, a significant challenge for removing some toxic organic molecules remains a challenge due to a need for metal-based catalytic properties owing to their rapid response. In the present study, we demonstrate the formation of hybrid structure AuNPs@MXene (Mo2CTx) during the sensitive detection of Au nanoparticle through MXene sheets without any surface modification, and subsequently its applications as an efficient catalyst for the degradation of 4-nitrophenol (4-NP), methyl orange (MO), and methylene blue (MB). The hybrid structure (AuNPs@MXene) reveals remarkable reusability for up to eight consecutive cycles, with minimal reduction in catalytic efficiency and comparable apparent reaction rate constant (Kapp) values for 4-NP, MB, and MO, compared to other catalysts reported in the literature.

Absorption-Based Rapid Acquisition of Single-Molecule Kinetics from Unstable Enzymes in Microdroplets.

Single-molecule catalysis reflects the heterogeneity of each molecule, providing a unique insight into the complex catalytic mechanism through the statistics of stochastic individuals. However, the present study methods for single-molecule catalysis are either complicated or have low throughput, limiting their rapid acquisition of single-molecule reaction kinetics with statistical significance. Here, a label-free imaging method is developed for the study of single-molecule catalysis in microdroplets with high throughput based on the absorption of the reaction molecules. A wide distribution of the catalytic reaction rate constant value of 238-2026 moleculess-1 is observed from 68 single enzymes. Interestingly, an exponential decayed distribution of the enzyme activity can be clearly observed due to the rapid denaturation of the enzymes. The denaturation mechanism of the Horse Radish Peroxidase (HRP)enzyme is clarified. It is revealed that the denaturation of each enzyme goes through a gradual decay rather than a truncated turn-off process from a single molecule point of view. This absorption-based method can be applied to most of the catalytic reactions with high throughput, which offers an indispensable route for the rapid statistical analysis of various single-molecule catalytic reactions, making it particularly suitable for the acquisition of catalytic kinetics from highly unstable enzymes.

Fe(VI) oxidation of synthetic phenolic antioxidants: Kinetics, influencing factors, transformation mechanism and toxicity

Synthetic phenolic antioxidants (SPAs) have been commonly used in industrial and domestic products to prevent the adverse effects of oxidants such as oxygen. However, attention to the removal of SPAs is scarcely attracted. In this paper, the removal kinetics, influencing factors, transformation mechanisms and toxicity in Fe(VI) oxidation of 18 SPA congeners were investigated in detail. Results showed that propyl gallate (PG), butylated hydroxyanisole (BHA), and tert-butylhydroquinone (TBHQ) had the highest reactivities with Fe(VI), while the reaction rate constant (kapp) value of 2,4-di-tert-butylphenyl 3,5-di-tert-butyl-4-hydroxybenzoate (UV120) was the lowest (221.3 M−1 s−1). A robust quantitative structure–activity relationship (QSAR) model between kapp and molecular structural descriptors of SPAs was established. The energy gap between the lowest unoccupied molecular orbital (ELUMO) and the highest occupied molecular orbital (EHOMO) was a vital parameter to determine the removal efficiencies of the SPA congeners. Furthermore, the numbers of oxygen atoms and alkyl groups in SPA structures also determined their reactivities with Fe(VI) to some extent. In addition, aqueous 2,6-di-tert-butyl-4-methylphenol (BHT, a representative of SPAs) could be efficiently removed with the increased amount of oxidant, and decreased substrate concentration and slightly alkaline conditions. Seventeen intermediates were identified, and oxidation routes including H-abstraction, single- and double-oxygen(s) transfer, and coupling were deduced. However, H-abstraction inevitably led to the generation of BHT-Q with higher toxicity than parent. These findings provide novel insights into the production and removal of SPA analogs.

Constructing the relationship between microstructure and piezocatalysis in (K, Na)NbO3 lead-free piezocatalyst

Piezocatalysis converts mechanical vibration into chemical energy and holds great potential for wastewater treatment and biomedical applications. Although the influence of microstructure on piezocatalysis is well recognized, its relationship has been rarely investigated in potassium sodium niobate ((K, Na)NbO3, KNN), an emerging lead-free and eco-friendly piezocatalyst. In this study, we modified the synthesis conditions of (K0.48Na0.52)NbO3-0.3 %Fe2O3 (KNN-Fe) material to produce KNN-Fe piezocatalysts with different microstructure characteristics. We then examined the relationship between microstructure and piezocatalysis by assessing the degradation of Rhodamine B (RhB) and methyl orange (MO) dyes. The KNN-Fe piezocatalyst with an 8 h-sand-ground shows the reaction rate constant (k) values of 79 × 10−3 min−1 and 27.12 × 10−3 min−1 for the degradation of RhB and MO, respectively. These values are 16 % and 303 % higher than those of the sand-ground-0 h sample. The enhanced piezocatalysis of the sand-ground-8 h sample stems from the increased specific surface area and oxygen vacancies, enhanced separation of electron-hole pairs, and higher carrier concentration. This study not only elucidates the relationship between microstructure and piezocatalysis in KNN materials but also suggests a potential approach for enhancing piezocatalytic activity.

β-Carotene and Lycopene Degradation Kinetics of Tarhana Dough During Convective Air Drying and Traditional Drying Methods

In this study, tarhana doughs were dried with convective air drying at 30, 40 and 50 oC temperatures and 0.5, 1.25 and 2 m/s air velocities, and with traditional drying (sun-drying method). By this way effects of drying air temperature and velocity on degradation kinetics of β-carotene and lycopene during air drying of tarhana samples were investigated and the results compared with traditional drying method. The degradation reaction of β-carotene and lycopene was found to be following the first-order kinetic model. The reaction rate constant values of the β-carotene degradation were determined in the range of 0.0003-0.0025 min-1, and the activation energy values were determined in the range of 6.15-49.05 kJ/mol. The reaction rate constant values of the lycopene degradation were determined in the range of 0.0001-0.0007 min-1, and the activation energy values were determined in the range of 20.5-34.3 kJ/mol. β-carotene and lycopene content of tarhana samples decreased with the increase in drying temperature, and the rate of degradation reactions of these components increased with the increase in temperature and air velocity. As a result, it was determined that β-carotene and lycopene were better preserved at 1.25 m/s air velocity at 30 oC.

Bifunctional quaternary magnetic composite as efficient heterojunctions photocatalyst for simultaneous photocatalytic visible light degradation of dye and herbicide pollutants from water and bacterial disinfection

In the present study, the magnetic Fe3O4/Ag2C2O4/Ag3PO4/Ag nanocomposite were prepared through a simple co-precipitation method by using calendula officinalis seed extract as a stabilizer. The fabricated quaternary photocatalyst was applied for to degrade food dye Brilliant Blue FCF (BB) and herbicide Paraquat (PQ) as contaminants at binary mixture in a batch and continuous flow-loop photoreactor under visible light irradiation and also the antibacterial properties was investigated. The fabricated nanocomposite was determined by XRD, FESEM, EDX, BET&BJH, UV-DRS, FT-IR and VSM methods to gain insight about structure, morphology, purity, surface area, optical, functional group and magnetic properties. The photoelectrochemical experiments, PL and DRS indicate the successful coupling of the active semiconductors. The degradation efficiency of BB and PQ was announced to be 88.9% and 92.72% under optimal conditions with a high reaction rate constant value (0.03 and 0.0326 min−1), respectively. The quaternary photocatalyst exhibited superior photocatalytic performance compared with Ag3PO4/Ag2C2O4 and Ag2C2O4. Various scavengers were used to explore the mechanism of photocatalytic performance and supports that O2−. and OH. is main active species in the degradation process of BB and PQ, respectively. Furthermore, the Fe3O4/Ag2C2O4/Ag3PO4/Ag also demonstrated bactericidal activity against Staphylococcus aureus (S. aureus) as gram-positive bacteria and Escherichia coli (E. coli) as gram-negative bacteria.

Reactivity of tert‐butylperoxyl radical with some phenylthiazolidine derivatives and probucol

AbstractThe hybrid molecule phenylthiazolidine derivatives and probucol were kinetically examined as antioxidants (AOs) in scavenging tert‐butylperoxyl radical (t‐BuOO•) with comparable to the reference AO, butylated hydroxytoluene (BHT). The anti‐t‐BuOO• reactivity of phenylthiazolidine derivatives and probucol was established using the direct kinetic electron paramagnetic resonance (EPR) technique with pulse reactant injection. Absolute values of the bimolecular reaction rate constants and antiradical capacities of the studied compounds were measured from −63 to 0°C. The main antiperoxylradical sites of the compounds under study were revealed.High removal ability of t‐BuOO• by (2‐(4‐hydroxyphenyl)thiazolidine), 4‐[thiazolidin‐2‐yl]benzene‐1,2‐diol, 2‐(4‐hydroxyphenyl)thiazolidine‐4‐carboxylic acid and probucol was connected with the reaction of hydrogen atom abstraction from phenolic OH group.Weaker antiperoxylradical reactivity of 2‐phenylthiazolidine was connected with the slower reaction of hydrogen atom abstraction from benzylic C–H bond in reference to nitrogen and sulfur atoms compared with the phenolic OH group. It is found that sulfide groups had much weaker participation in antiperoxylradical reactivity of the studied compounds. It is concluded that removal of alkylperoxyl radicals by oxidizable phenylthiazolidine derivatives and probucol may partially account for biological activity of their compounds.

Drug release kinetics of capsule shells from seaweed carrageenan extract (Eucheuma cottonii) and potato starch as a gelling agent

BackgroundCapsules are created to put a drug or active pharmaceutical ingredient in an elegant, odorless, tasteless, easy-to-swallow and to-fill shell commonly produced from gelatin. Therefore, carrageenan is one of the other natural ingredients that can replace gelatin. This study aims to make capsule shells from carrageenan seaweed (Eucheuma cottonii) with variations in carrageenan composition and temperature using potato starch as a gelling agent with the addition of PEG as a plasticizer and to determine the kinetics model of the drug release system from the capsules that have been made.ResultsIn the research there are two variations namely composition and temperature. The capsule shell dissolution test results were calculated using kinetic models of order 0, order 1, Higuchi, and Korsmeyer-Peppas. The result on zero order is that at the C composition and temperature 55 ºC variations obtained the reaction rate constant (k) are 1.05 and 1.27 min respectively. While in first order obtained the reaction rate constant of 4.59 × 10–2 and 2.06 × 10−2 min−1 respectively at variations in capsule D composition and temperature of 60ºC. In the Higuchi model, the correlation coefficient for composition variation is better than temperature variation of 0.92. In the Korsmeyyer-Peppas model, the value of reaction rate constant (k) at composition C and temperature of 55 ºC variations are 1.41 × 10–2 and 9.49 × 10−3 min−n.ConclusionsThe Korsmeyyer–Peppas kinetic model is suitable for illustrating the drug release kinetics of capsule shells from seaweed carrageenan extract (Eucheuma cottonii) and potato starch as a gelling agent.

One‐pot synthesis of CuO/TiO2 nanocomposites for improved photocatalytic hydrogenation of 4‐nitrophenol to 4‐aminophenol under direct sunlight

AbstractThe excellent photocatalytic hydrogenation of 4‐nitrophenol (4‐NP) to 4‐aminophenol (4‐AP) with NaBH4 in the aqueous medium is still a big challenge. Herein, we report a facile one‐pot evaporation‐induced self‐assembly (EISA) method to synthesize a series of CuO/TiO2 nanocomposites. The as‐synthesized CuO/TiO2 photocatalysts exhibit remarkable catalytic activity under direct sunlight in selective hydrogenation of 4‐nitrophenol (4‐NP) to 4‐aminophenol (4‐AP) due to the synergistic interaction of guest copper nanoparticles with host titanium dioxide (TiO2) species. Especially, 5 wt% CuO/TiO2 nanocomposite revealed superior reaction rate constant (k) value (0.306 min−1) when compared to 3 wt% CuO/TiO2 (0.192 min−1) and 7 wt% CuO/TiO2 (0.240 min−1). Moreover, several characterization techniques (XRD, TEM, N2 adsorption–desorption isotherm, DRS, and XPS) were executed to deeply investigate the effect of copper content on the bulk and interfacial properties of the catalysts. The characterization results proved that the superior photocatalytic hydrogenation over 5 wt% CuO/TiO2 catalyst can be ascribed to moderate CuO loading as well as even dispersion of CuO species on the surface of active TiO2 host, which can largely improve the light absorption ability within visible light region. Besides, the 5 wt% CuO/TiO2 catalyst exhibits remarkable recyclability and durability, retaining its superior activity (above 95%) up to several repeating cycles, proving its practical applicability for hydrogenation reactions at domestic and industrial levels.

Efficient Conversion of Biomass‐Derived Furfural to Tetrahydrofurfuryl Alcohol over Co3O4−C Nanocomposite Catalyst at Mild Conditions

AbstractDue to the depletion of fossil fuel resources, catalytic conversion of biomass into liquid fuels and valuable compounds has become an attractive field of research. Tetrahydrofurfuryl alcohol (THFAL) is an important platform molecule in both industrial and pharmacological fields, and catalytic hydrogenation of furfural (FA) to THFAL is a sustainable process. However, an active and stable catalyst for the direct hydrogenation of FA to THFAL under milder conditions is still a challenge. Accordingly, herein, we investigated a high‐valence metal catalyst (Co3O4−C) for the hydrogenation of FA to THFAL using sodium borohydride (NaBH4) as the H source. Under optimal reaction conditions (that is, 0.05 g Co3O4−C‐700 in an aqueous solution, 5 mmol NaBH4, 60 °C, and 3 h), 88.5 % THFAL was produced over Co3O4−C‐700. The kinetic study revealed that furfuryl alcohol was generated as an intermediate during the hydrogenation of FA. Additionally, the reaction followed pseudo‐first order kinetics, and the reaction rate constant (k) values were .80, 3.41, 3.45, and 5.55 h−1 at 30, 40, 45, 50, and 60 °C, respectively. From the slopes of the Arrhenius plot, the activation energy was determined to be 22.02 kJ mol−1, indicating high activity of the catalyst for the reaction. Moreover, Co3+ and smaller sizes of Co3O4 nanoparticles contributed to the activity of Co3O4−C‐700. We believe that the metal oxide catalyst developed herein can be used for various biomass conversions.

High-Pressure Depolymerization of Poly(lactic acid) (PLA) and Poly(3-hydroxybutyrate) (PHB) Using Bio-Based Solvents: A Way to Produce Alkyl Esters Which Can Be Modified to Polymerizable Monomers.

The polyesters poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) used in various applications such as food packaging or 3D printing were depolymerized by biobased aliphatic alcohols-methanol and ethanol with the presence of para-toluenesulphonic acid (p-TSA) as a catalyst at a temperature of 151 °C. It was found that the fastest depolymerization is reached using methanol as anucleophile for the reaction with PLA, resulting in the value of reaction rate constant (k) of 0.0425 min-1 and the yield of methyl lactate of 93.8% after 120 min. On the other hand, the value of constant k for the depolymerization of PHB in the presence of ethanol reached 0.0064 min-1 and the yield of ethyl 3-hydroxybutyrate was of 76.0% after 240 min. A kinetics study of depolymerization was performed via LC-MS analysis of alkyl esters of lactic acid and 3-hydroxybutanoic acid. The structure confirmation of the products was performed via FT-IR, MS, 1H NMR, and 13C NMR. Synthesized alkyl lactates and 3-hydroxybutyrates were modified into polymerizable molecules using methacrylic anhydride as a reactant and potassium 2-ethylhexanoate as a catalyst at a temperature of 80 °C. All alkyl esters were methacrylated for 24 h, guaranteeing the quantitative yield (which in all cases reached values equal to or of more than 98%). The methacrylation rate constants (k') were calculated to compare the reaction kinetics of each alkyl ester. It was found that lactates reach afaster rate of reaction than 3-hydroxybutyrates. The value of k' for themethacrylated methyl lactate reached 0.0885 dm3/(mol·min). Opposite to this result, methacrylated ethyl 3-hydroxybutyrate's constant k' was 0.0075 dm3/(mol·min). The reaction rate study was conducted by the GC-FID method and the structures were confirmed via FT-IR, MS, 1H NMR, and 13C NMR.

Renewable and eco-friendly ZnO immobilized onto dead sea sponge floating materials with dual practical aspects for enhanced photocatalysis and disinfection applications

In this study, we have investigated the role of natural dead sea sponge (DSS, Porifera) as a three-dimensional (3D) porous host substrate for the immobilization of nanostructured ZnO material towards the development of ZnO based floating photocatalysts for efficient removal of methylene blue (MB) dye under the illumination of sunlight. After photodegradation, the treated water after dye degradation contains several pathogens, different disinfectants or chemical reagents that are essentially used. This is not the case for DSS as it can naturally kill any pathogens during the wastewater treatment process. To explore these functions, ZnO nanosheets were incorporated onto DSS via hydrothermal protocol and the as prepared ZnO/DSS hybrid material exhibited approximately ∼100% degradation efficiency for the removal of MB. Importantly, the degradation kinetics associated with the fabricated ZnO/DSS was remarkably accelerated as evidenced by the high values of degradation reaction rate constants (3.35 × 10–2 min−1). The outperformance of ZnO/DSS could be attributed to the adsorption caused by its 3D porous structure together with the high rapid oxidation of MB. Furthermore, the high charge separation of electron–hole pairs, natural porosity, and abundant catalytic sites offered by the hybrid ZnO/DSS floating photocatalyst have enabled quantitative (∼100%) degradation efficiency for MB. Finally, the excellent reusability results confirm the feasibility of using natural ZnO/DSS-based photocatalyst for practical solution of wastewater treatment and other environmental problems.

Kinetika Reaksi Resin Immobilized Photocatalyst Technology (RIPT) TiO2 Sebagai Bahan Alternatif Pengolahan Limbah Cair Tahu

Liquid waste from the tofu industry contains a lot of organic matter, the high content of this organic material will result in high BOD and COD values ​​in the waters and can have a bad impact if not handled properly. One alternative that is commonly used to overcome this problem is to use a photocatalyst degradation method. This study aims to determine the reaction kinetics which includes the determination of the reaction rate constant and the reaction order in removing the COD content of the resin-immobilized TiO₂ photocatalyst. This study presents the reaction kinetics of RIPT with catalyst, TiO2, catalyst mass (10gr, 20gr, 30gr), and RIPT mass (5gr, 10gr, 15gr). This research was conducted by making immobilized TiO2 photocatalyst resin and then entering 1000 ml of tofu industrial waste and the obtained RIPT-resin into the reactor in which stirring occurred using a test jar. Based on the results of the study, the best value for the reaction rate constant was obtained by the mass variation of RIPT (15gr). Meanwhile, the best value constant of reaction rate was obtained by mass variation of 30 gram TiO2 catalyst, with the result that the reaction rate constant value of RIPT- and RIPT-TiO2 30 grams was 0.0101 minute-1.