Order Reaction Rate Constants Research Articles

Degradation and mineralization of anti-cancer drugs Capecitabine, Bicalutamide and Irinotecan by UV-irradiation and ozone

The degradation of three anti-cancer drugs (ADs), Capecitabine (CAP), Bicalutamide (BIC) and Irinotecan (IRI), in ultrapure water by ozonation and UV-irradiation was tested in a bench-scale reactor and AD concentrations were measured through ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). A low-pressure mercury UV (LP-UV) lamp was used and degradation by UV (λ = 254 nm) followed pseudo-first order kinetics. Incident radiation in the reactor was measured via chemical actinometry using uridine. The quantum yields (φ) for the degradation of CAP, BIC and IRI were 0.012, 0.0020 and 0.0045 mol Einstein−1, respectively. Ozone experiments with CAP and IRI were conducted by adding ozone stock solution to the reactor either with or without addition of tert-butanol (t-BuOH) as radical quencher. Using this experimental arrangement, no degradation of BIC was observed, so a semi-batch setup was employed for the ozone degradation experiments of BIC. Without t-BuOH, apparent second order reaction rate constants for the reaction of the ADs with molecular ozone were determined to be 3.5 ± 0.8 ∙ 103 L mol−1 s−1 (CAP), 7.9 ± 2.1 ∙ 10−1 L mol−1 s−1 (BIC) and 1.0 ± 0.3 ∙ 103 L mol−1 s−1 (IRI). When OH-radicals (∙OH) were quenched, rate constants were virtually the same for CAP and IRI. For BIC, a significantly lower constant of 1.0 ± 0.5 ∙ 10−1 L mol−1 s−1 was determined. Of the tested substances, BIC was the most recalcitrant, with the slowest degradation during both ozonation and UV-irradiation. The extent of mineralization was also determined for both processes. UV irradiation was able to fully degrade up to 80% of DOC, ozonation up to 30%. Toxicity tests with Daphnia magna (D. magna) did not find toxicity for fully degraded solutions of the three ADs at environmentally relevant concentrations.

Key role of carbon as an efficient electron bridge in CuO@C@Fe2O3 for enhancing H2O2 activation during photo-assisted Fenton-like reaction

The Fe3+/Fe2+ cycle has been identified as the rate-limiting step in the Fenton system, and many efforts have been made to promote the Fe3+ reduction via external electrons provided by various electron donors. However, how to design an efficient electron transport pathway and then inhibit the invalid electron shuttle has been largely underestimated. In this study, two kinds of heterogeneous Fenton catalysts of CuO@Fe2O3 and CuO@C@Fe2O3 were prepared. The key role of carbon in transporting electrons as an electron bridge and its enhancement mechanism in photo-assisted Fenton-like performances were explored in detail. Compared with CuO@Fe2O3, the removal efficiency of tetracycline (TC) and the corresponding pseudo-first order reaction rate constants over CuO@C@Fe2O3 increased significantly from 88.6 % and 0.1054 min−1 to 99.7 % and 0.2058 min−1, respectively. Based on a series of probe experiments, visible light irradiation can promote the reduction of Cu2+ to Cu+, then the carbon in CuO@C@Fe2O3 can effectively transfer electrons from Cu+ to Fe3+, enhancing the Fe3+/Fe2+ cycle and the following Fenton-like efficiency. Since more ·OH while less ∙O2- was produced over CuO@C@Fe2O3, which further supports the fact that the enhanced Fe3+/Fe2+ cycle was due to the transfer electron from Cu+ to Fe3+ instead of the Haber-Wiss mechanism. Hence, this study provides new insight for effectively improving the transfer efficiency and effective utilization of electrons in Fenton systems.

Enhanced photocatalytic gaseous formaldehyde degradation using N-CQDs/OVs-TiO2 composite under visible light: Unraveling the synergistic effects of N-CQDs and oxygen vacancies

Limited utilization of photogenerated charge carriers in titanium dioxide under visible light have hinder its application development. To address this challenge, a novel N-doped carbon quantum dots (N-CQDs) and oxygen vacancies (OVs) synergistically decorated on TiO2 (P25) was synthesized through a facile one-step hydrothermal method. Under visible light irradiation, the first order reaction rate constants of formaldehyde (HCHO) photocatalytic oxidation by OVs-TiO2 and N-CQDs/OVs-TiO2 was significantly higher than that of pristine P25, with 10.1 and 16.7 folds increase, respectively. Characterization results confirmed the generation of OVs on the surface of N-CQDs/TiO2 composite. The optical and electrochemical experiments suggested the electron capture center effect of OVs and the properties of N-CQDs in unique up-converted photoluminescence, efficient charge separation, as well as significant adsorption in visible light region. In addition, the work function also clarified that photoelectrons could transfer from N-CQDs to OVs-TiO2. Furthermore, different relative humidity and electron paramagnetic resonance (EPR) experiments demonstrated that the hydroxyl radical (•OH) was the dominant reactive radical in HCHO photodegradation. The •O2− could also enhance the photodegradation efficiency of HCHO. This work provides an in-depth understanding on the complementary roles of N-CQDs and OVs and is helpful for designing metallic oxide photocatalysts for volatile organic compounds removal.

Comparative study of metal nanoparticles anchored TiO2 using polyoxometalate intermediate in photodegradation of azo dye pollutant in aquatic environments

Herein, metal nanoparticles (Au, Ag, and Pt) are locally deposited on TiO2 with an UV-switchable polyoxometalate intermediate to achieve highly active photocatalyst nanohybrids. The successful preparation of these nanohybrids was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), Zeta potential (ZP), and UV–visible spectroscopy. TEM images showed the anchoring of metal nanoparticles of an average size of 20 nm on the TiO2 surface. A comparative study revealed that the bandgap energy was reduced in the order of Pt@PW-TiO2 (2.90 eV) > Ag@PW-TiO2 (2.95 eV) > Au@PW-TiO2 (3.05 eV). Likewise, the photocatalytic efficiency of fabricated nanohybrids was investigated in the degradation of reactive blue 19 (RB19), an azo dye model, under UV–visible light illumination and different experimental conditions. Optimal photodegradation occurred at pH = 3.8 with 0.33 gL−1 of photocatalyst exposed to light for 60 min. Under optimal conditions, the maximum and minimum photodegradation abilities were observed using Pt and Au deposited hybrids. A kinetic study of RB19 photodegradation was also conducted, resulting in pseudo-first order reaction rate constants of 0.0203, 0.025, and 0.0808 min−1, respectively, for the Au@PW-TiO2, Ag@PW-TiO2, and Pt@PW-TiO2 nanohybrids. Finally, the most probable mechanism for RB19 degradation using prepared photocatalysts is presented.

Photocatalytic degradation of gentamicin using TiO2 nanoparticle driven by UV light irradiation

Antibiotics have contributed to enhance life expectancy in underdeveloped countries by reducing mortality rate, but the hazards connected with antibiotic pollution are largely harming people. The photocatalytic degradation of gentamicin utilizing Titanium oxide nanoparticles (TiO2nps) using visible and UV light has been studied. TiO2nps was synthesized using the co-precipitation method and calcined at 600 °C. XRD study confirmed the phase formation and Raman study confirmed the structure of TiO2nps. UV–Vis’s absorption study was performed in which a broad peak was obtained between 300 and 600 nm. The degradation percentage for the photocatalytic study was found to be 51 %, 84 %, and 95 % under dark, visible light, and UV light, respectively. The pseudo-first order reaction rate constant was calculated for the sample exposed to UV light, and was found to be 0.0158. In the cyclic study, high degradation percentage of more than 80 % was obtained even after four cycle of degradation.

Hydrogen Evolution Reaction By Metal-Free Poly-Neutral Red Electrocatalyst

While electric power supply by renewable sources such as solar and wind has become viable for their significant cost reduction, its intermittency demands urgent development of large scale storage technologies. Although conversion of electrical energy into storable hydrogen via electrolysis of water is ideal, noble metals and their oxides are used as electrocatalysts for their activities and stabilities. Alternative electrocatalysts out of abundant elements are needed for sustainable technological development.Recently, some metal-free organic conductive polymers with hydrogen-bonding capabilities were found to exhibit high electrocatalytic activities towards hydrogen evolution reaction (HER) [1,2]. We have succeeded electropolymerization of neutral red (NR) resulting in a formation of conductive poly-NR (PNR) that shows a relatively high HER catalytic activity [3]. PNR possesses hydrogen-bonding N atoms as annelated in the phenazine aromatic system as well as those in the amino substituents. Electrochemical analysis combined with in situ spectroscopy as well as DFT calculation was performed to clarify the mechanism and kinetics of HER electrocatalysis by PNR.This films of PNR were obtained by electropolymerization on F-doped SnO2 coated conductive glass (FTO, Asahi Glass) and SIGRATHERM® GFA5 Carbon felt with potential cycling between -0.2 and 1.2 V (vs. Ag/AgCl) at 50 mV s-1 for 50 times in a 5 mM NR - 0.1 M H2SO4 aqueous solution under N2. Polyaniline (PANI) was also obtained by the same method for comparison. The HER catalysis was evaluated by linear sweep voltammetry (LSV) in a 1 M trifluoromethanesulfonic acid (TfOH) under N2. The film samples were characterized by Fourier transform infrared spectroscopy (FT-IR), UV-visible spectroscopy. In-situ UV-visible spectroelectrochemical monitoring of the reaction intermediate was carried out to determine the rate of HER.PNR undergoes a pseudo-reversible reduction that shifts -61.8 mV/pH under acidic conditions and HER takes off right at this point (Fig. 1, a). Coupling of the same number of protons / electrons is expected as the electrochemical stoichometry from the observed Nernstian relationship, namely, resulting in a singly reduced PNR-H or doubly reduced PNR-H2 as depicted in Fig. 1 b. Protonation of N atoms was reasonably expected and also supported by the DFT calculation. The hydrogen atoms stabilized in the reaction intermediate can be associated to release H2 (Tafel mechanism) to complete the cycle of electrocatalysis of HER.Reduction of PNR in fact is associated with a color change. The broad reddish absorption of PNR peaking at around 500 nm attenuates to change the color to a pale yellow by constantly applying -0.15 V vs. RHE to produce PNR-H and/or PNR-H2 state as shown in Fig. 1c. Gradual recovery of the original red PNR was observed under open circuit under N2, associated with the H2 release. Thus, the rate of the spectral change is analyzed to determine the rate of the Tafel process. Pseudo-first order reaction rate law can be applied as proton is abundant and its concentration is constant, so that the rate of HER (r H2) is simply described as the rate of consumption of PNR-H and/or PNR-H2 as, r H2=-dC PNR-H2/dt =-kt (1)The ratio of PNR-H and PNR-H2 as compared to their initial amount (x PNR-red) was defined from the absorbance at 545 nm before and after reduction as, x PNR-red = C PNR-red/C 0-PNR-red = exp (-kt) (2)Good fitting of the experimental data was obtained to yield a pseudo-first order reaction rate constant of 9.98×10-4 s-1 for this rate-limiting step.

How effective aerated continuous electrocoagulation can be for tetracycline removal from river water using aluminium electrodes?

The study assessed the effects of aeration on continuous electrocoagulation (EC) for tetracycline (TCL) removal from river water. Influence of hydraulic retention time (HRT) and initial drug concentration on treatment efficiency was tested. Best conditions for continuous EC operation were 12 min HRT, electrode spacing 2 cm, 9 V, and Al–Al electrode combination. Highest COD removal with non-aerated EC was 59.4% at 1 mg L−1 initial TCL concentration and further increasing TCL concentration decreased COD removal efficiency. Maximum TCL removal was 66.6% at 10 mg L−1 initial TCL concentration with non-aerated EC. Aerated EC enhanced COD and TCL removal to 61.4% and 71.5%, respectively. In XRD and FTIR spectra no new peaks were detected following EC treatment. XRD, FTIR and FESEM-EDS data supported that significant removal of TCL occurred by charge neutralization, entrapment, adsorption and precipitation driven by Al (OH)3 flocs. Pseudo-second order reaction rate constants explained the kinetics of TCL removal from river water. Sludge volume produced with continuous mode EC non-aerated and aerated EC was 31 cm3 and 39 cm3, respectively. Operating cost was estimated to 0.018 US$/m3 for non-aerated EC and 0.025 US$/m3 for aerated EC. EC can be augmented by aeration for enhanced removal of TCL from river water.

Oxidation of bromide by heat-activated persulfate – Effects of temperature and the organic matter surrogate phenol on kinetics and stoichiometry

• Oxidation of persulfate by sulfate radical affects persulfate decomposition kinetics. • Bromide oxidation to bromate was hindered by phenol. • Sulfate radicals reacting with Br-species decreased at higher temperature. • Insoluble phenol oxidation byproducts formation is favored at high temperature. Reaction mechanisms of sulfate radical with bromide and organic substances can be largely altered at elevated temperature in heat-activated persulfate process due to different activation energies. This study investigated kinetics and stoichiometry of bromide oxidation in the heat-activated persulfate process. We postulated that reaction of sulfate radical with persulfate, which has relatively low reaction rate (6.3 × 10 5 M −1 s −1 ), may become an important reaction at elevated temperatures. Persulfate decomposition was inhibited in the presence of sulfate radical scavenger phenol at low temperature (40 °C) whereas phenol affected persulfate decomposition only at < 50 °C but not at higher temperatures. This was because the second order reaction rate constant of sulfate radical with persulfate became higher (assumed as 10 10 M −1 s −1 ) than with phenol at a temperature > 50 °C, which can be explained by a high activation energy (estimated activation energy: 311 kJ/mol). Bromate formation was inhibited in the presence of phenol. However, phenol oxidation was not affected by the presence of Br − , even though Br − reacts faster with sulfate radicals than phenol and was present in excess. This indicated that formed reactive bromine species such as Br and Br 2 − oxidize phenol under reformation of bromide. Formation of insoluble products was also observed indicating polymerization of phenol. This can be explained by lack of dissolved oxygen under conditions of heat-activation.

Reaction kinetics of dissolved black carbon with hydroxyl radical, sulfate radical and reactive chlorine radicals

As an important component of dissolved organic matter (DOM), dissolved black carbon (DBC) which is characterized of abundant aromatic and oxygen-containing functional groups, is widely distributed in aquatic environments. Its presence may hinder the oxidation of organic micro-pollutants during advanced oxidation processes (AOPs) via free radicals scavenging effect. However, the second-order reaction rate constants of DBC with different free radicals including hydroxyl radical (OH•), sulfate radical (SO4•-), reactive chlorine radicals (RCR) are unknown and the relationship between the chemical composition of DBC and the second-order reaction rate constants during different AOPs (UV/H2O2, UV/PDS, UV/Chlorine) is also unclear. In this study, a plant-derived DBC was extracted from wheat biochar and fractionated according to molecular weight (i.e., <10 k, <3 k, and < 1 k Da). The second order rate constants of DBC reaction with different free radicals were determined by competitive kinetic method. Besides, the chemical composition of DBC was revealed by ultraviolet-visible (UV–Vis) spectroscopy, fluorescence excitation-emission-matrix (EEM) spectroscopy Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with statistical analysis. The results showed that the second-order rate constants decreased as the molecular weight increased. For the <1 k Da DBC, the kDBC-OH•, kDBC-SO4•-−, kDBC-RCR were (1.83 ± 0.06) × 104, (7.60 ± 0.21) × 103, and (1.71 ± 0.13) × 104 L·mgC−1·s−1, which were 1.98, 2.19, 1.43 times of that for the <10 k Da fraction and 1.38, 1.36, 1.24 times of that for the <3 k Da fraction in UV/H2O2, UV/PDS and UV/Chlorine processes. In addition, the results of chemical composition analysis showed that DBC mainly contained humic substances and was rich in O-containing functional groups such as CO. The second order reaction rate constants of DBC with different free radicals decreased with increasing the molecular weight of DBC due to the more aggregated structure of the small molecules that the inner carbon of DBC was not easily exposed to free radicals.

Photocatalytic reductive applications of C-doped ZrO2/PANI composite towards Cr(VI)

Carbon doped zirconium oxide polyaniline, C-ZrO2/PANI was synthesised for application in the photocatalytic reduction of Cr(VI) under visible light irradiation. The carbon doping agent applied was carboxymethyl cellulose. C-ZrO2 was obtained via the precipitation method. Coupling of the polyaniline to the C-ZrO2 occurred by in situ oxidative polymerization to obtain the C-ZrO2/PANI composite. XPS and EDS showed presence of C, Zr, O, N in the C-ZrO2/PANI sample. The physiochemical characteristics of the photocatalyst such as a large surface area of 31,47 m2/g, good charge separation were important aspects in the adsorption and subsequent Cr(VI) reduction. Band edge positions for the C-ZrO2/PANI deduced from UV–Vis DRS and Mott-Schottky plot showed that the lowest unoccupied molecular orbital (LUMO) of PANI was below the C-ZrO2 conduction band (CB). Further, photogenerated electrons from LUMO were transferred to C-ZrO2 CB and were involved in the generation of superoxide radicals, •O2−, which were critical in Cr(VI) reduction to Cr(III). Comparably the photocatalyst, C-ZrO2/PANISDS, prepared in the presence of surfactant sodium dodecyl sulfate (SDS) indicated diminished photocatalytic reduction of Cr(VI). From the photocatalytic results, performances of the photocatalysts were in the order C-ZrO2/PANI > PANI > C-ZrO2/PANISDS. Photocatalytic results revealed that 100% of 20 mg/L Cr(VI) was reduced by C-ZrO2/PANI within 70 mins at pH 2. The first order reaction rate constant was 0.0309 min−1. The photocatalyst can be reused for 4 cycles without excessive loss of efficiency and with maintained stability.

Insights into a packed bubble column for removal of several ozone-persistent TrOCs by ozonation: removal kinetics, energy efficiency and elimination prediction

Ozonation is an efficient method to remove trace organic contaminants (TrOCs) from (waste)water. However, high ozone dose requirement and energy consumption are still limiting its wider application for ozone-persistence TrOCs elimination. In this study, a packed bubble column is designed to enhance the ozone gas-liquid mass transfer and consequentially improve ozone and hydroxyl radical (OH) exposures. An increase of 5–31% removal for five selected ozone-persistence TrOCs was observed in the packed bubble column in comparison to an unpacked bubble column under the same experimental settings. The energy consumption (EEO) for 90% TrOCs removal in the packed column was in range of 0.99–2.76 kWh/m3, which was 5–48% decrease after the use of packing materials. A kinetics-based approach based on the correlation between the concentration of target compounds, the second order reaction rate constants of these compounds with ozone and OH and the ozone and OH exposures was used to predict TrOCs removal. The predicted removal was consistent the measured removal, indicating that this prediction approach can be applied in packed system.

Heterogeneous activation of peroxymonosulfate by Co3O4 loaded biochar for efficient degradation of 2,4-dichlorophenoxyacetic acid

Carbon-based catalysts have the advantage of biological cleaning and cost-effectiveness in water treatment. This work used a two-step calcination method to prepare a novel nanometer composite material (CBC-1), where flake-like Cobalt oxide (Co 3 O 4 ) loaded on rice husk biochar. CBC-1 was used to activate PMS and degrade 2,4-dichlorophenoxyacetic acid (2,4-D) in the water phase. SEM, XRD, FT-IR, BET, XPS, EPR and other characterization methods showed that both sulfate radical and hydroxyl radical were involved in 2,4-D degradation. Both the high hydroxyl (-OH) content and Co (II) of the catalyst are beneficial to the activation of PMS. The pseudo-first order reaction rate constant of CBC-1 was 5.3 and 16 times that of pure Co 3 O 4 and biochar. This research provides new ideas for the application of carbon-based materials in the water treatment process and achieves the goals of treating waste water polluted by pesticides effectively and resource utilization of agricultural waste. • Provided a new view for the waste utilization of rice husk. • Enhanced the catalytic activity of Co 3 O 4 with rice husk biochar added. • CBC-1/PMS system exhibited satisfactory degradation efficiency of 2,4-D within 10 min. • The higher hydroxyl content of CBC-1 is helpful for enhancing the catalytic ability.

Construction of Fe3O4@β-CD/g-C3N4 nanocomposite catalyst for degradation of PCBs in wastewater through photodegradation and heterogeneous Fenton oxidation

Herein, a multifunctional magnetic β-cyclodextrin/graphitic carbon nitride catalyst (Fe3O4@β-CD/g-C3N4) was fabricated for PCBs degradation in wastewater. The catalysts were investigated using various characterization methods including X-ray diffractometry, field emission scanning electron microscopy, vibrating sample magnetometry and UV–Vis diffuse reflectance spectroscopy et al. As-synthesized Fe3O4@β-CD/g-C3N4 displayed the superior catalytic activity, and the degradation efficiency of six PCBs was 77%–98% at 55 min, with pseudo-first order reaction rate constants were in the range of 0.027–0.065 min−1. The super synergy of photodegradation and heterogeneous Fenton oxidation was 2.1–4.6 times more efficient than that photodegradation or heterogeneous Fenton oxidation alone. Fe3O4@β-CD/g-C3N4 could be reused for at least 6 cycles without significant deterioration to its catalytic activity. Several reaction intermediates were identified using GC-MS/MS. The products of the last stage of the reaction were alkanes, aldehyde, ketone and ester, which were formed via ring opening, dechlorinating and isomerization reactions. For PCBs degradation, •OH played a major role, •O2− played a secondary role, 1O2, h± and e− played minor roles based on reactive species trapping experiments. The catalytic performance of the Fe3O4@β-CD/g-C3N4 − H2O2 − visible light system towards degradation of PCBs in river water and municipal wastewater was 89–100% and 69–92%, respectively, which means the Fe3O4@β-CD/g-C3N4 has great potential for environmental remediation.

Study the Behavior of Activity and Express for Enzymes

Enzymes are be defined as soluble, colloidal, organic catalysts which are produced by living cells.Enzymes are biologic catalysts to accelerate the rate of biochemical reactions.in this study Quantification of the Enzyme Activity, Where: E = enzyme concentration; S = substrateconcentration; ES = enzyme-substrate complex concentration; k1, k3= 1st order reaction rate constants(t-1); P = product concentration; k2= 2nd reaction rate constant (M-1.t-1).At first, it must be stressed thatthe formation of ES (enzyme-substrate complex) is an obligatory step to any type of enzyme-catalyzedreaction. The ES, depending on the reaction conditions, can form the product (forward reaction) ornot (reward reaction). The immobilization technique allowed a more frequent use of biomaterials inindustry, therapeutics (confection of subcutaneous capsules for controlled delivering of hormones), andlab analysis (automatic dosing equipments, enzyme electrode, biosensors and enzyme immunoassays).In industry, the use of glucose isomerase for the conversion of glucose into fructose (high fructosecorn syrup), the aminoacylase for the separation of racemic mixture of amino acids, microbial lipase intriglyceride hydrolysis, and the lactase for removing lactose from milk and/or whey are stressed.

Fabrication of ZIF-8 decorated copper doped TiO2 nanocomposite at low ZIF-8 loading for solar energy applications

The effects of crystallization time and amount of Zeolitic Imidazolate Framework-8 (ZIF-8) on the photocatalytic activity of ZIF-8 decorated copper (Cu) doped titania (TiO2) (ZIF-8/Cu-TiO2) powders were investigated in this study. The formation of nanocomposite structure of ZIF-8 crystals grown over the surface of core Cu-TiO2 particles containing heterojunction sites was observed at low ZIF-8 level. Powders containing ZIF-8 in the 5–46% range (weight basis) were synthesized and their activities in the photocatalytic degradation of an organic dye molecule were evaluated. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (ATR-FTIR), thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM) analyses indicated that ZIF-8/Cu-TiO2 nanocomposite can be prepared at low levels of ZIF-8. HR-TEM images of 46% ZIF-8/Cu-TiO2 showed that Cu-TiO2 particles act as a core and ZIF-8 crystals grow over the surface of Cu-TiO2 particles during crystal growth and Cu-TiO2 particles were almost completely covered with ZIF-8 crystals. Photocatalytic activity increased with decreasing ZIF-8 level which was attributed to the formation of heterojunctions due to partial coverage of TiO2 surface. The 1st order reaction rate constant of ZIF-8/Cu-TiO2 nanocomposite containing 5% ZIF-8 was found to be 4 and 1.4 times that of bare ZIF-8 and Cu-TiO2, respectively. Partial coverage of TiO2 surface with ZIF-8 crystals lead to the formation of light exposed ZIF-8/Cu-TiO2 heterojunction sites for the enhanced degradation of the dye molecule. The presence of ZIF-8 in the nanocomposite also increased the adsorption of the organic dye by the interaction with open Zn2+ metal sites of ZIF-8 on the nanocomposite surface. This study revealed that ZIF-8/Cu-TiO2 nanocomposites could be prepared at low ZIF-8 levels and short growth times with higher photocatalytic activities than their constituents and nanocomposites prepared at higher ZIF-8 levels and longer growth times.

Shelf-Life Stability of Ready-to-Use Green Rooibos Iced Tea Powder-Assessment of Physical, Chemical, and Sensory Properties.

Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles.

A simplified fabrication of α-NiMoO4 via greener approach: Properties and its photocatalytic activity

The research work demonstrates the facile fabrication of nickel molybdates (NiMoO4) nanocatalyst via greener approach using moringa oleifera extract as chelating agent. The phase and crystalline structure, functional groups, morphology were characterized using characterization tools. The XRD patterns confirms the monoclinic phase structure of α-NiMoO4 with the crystallite size of ~18 nm. The existence of Ni 2p, Mo 3d and O1s energy levels characteristics in the synthesized nanocatlayst was determined from the XPS analysis. Then the prepared nanocatalyst (α-NiMoO4) used as active material to degrade the methylene blue (effluent dye) under visible light and solar radiation. The photo-degradation efficiency of MB achieved to be 91% over the optimal nanocatalyst (NiMoO4) under solar radiation condition over 2 h and 81% for visible light under the same condition. Pseudo first order reaction rate constants of NiMoO4 for both visible light and solar light irradiation are determined to be 0.01387 min−1 and 0.01902 min−1, respectively.

Comparison of Kinetics of Cr (III) Ions Removal from Wastewater Using Raw and Activated Montmorillonite Minerals

In this study, kinetics of the removal of Cr (III) from the waters by adsorption have been investigated using montmorillonite natural clay that was obtained from the vicinity of Narman, Erzurum in Turkey. Activation energy, thermodynamic values and adsorption kinetics were determined. In addition, the trials were repeated by subjecting to the same adsorbent activation process. The values ​​found for these two adsorbents were compared. As a result of the experiments, the parameters affecting the adsorption kinetics were examined. It was determined that the adsorption process could be best depicted by pseudo second order reaction kinetics. Using pseudo second order reaction rate constants, ΔH° = -25.791 kJ mol-1 and ΔS° = 106.19 joule mol-1 were calculated for raw adsorbent. For the activated adsorbent, ΔH° = -18,806 kJ mol-1 and ΔS° = 79.37 joule mol-1 were calculated. That ΔG° increases as temperature increases indicates; adsorption is more spontaneous at high temperatures. Negative ΔH° values show that the reaction is exothermic. The positive values of ΔS° indicate increased randomness at the adsorbent/solution interface during the adsorption of chrome.

Response surface methodology-based fabrication of boron-doped diamond electrodes for electrochemical degradation of guaifenesin in aqueous solutions

In this study, a boron doped diamond (BDD) electrode (RSM2), fabricated at a boron/carbon (B/C) ratio = 0.75%, a carbon/hydrogen (C/H) ratio = 1.00%, and a reaction chamber pressure (P) = 5.00 torr, exhibited the best performance in terms of electrochemical degradation of guaifenesin [guaiacol glyceryl ether (GGE)] and total organic carbon (TOC) removal among 11 BDD electrodes prepared according to the response surface methodology (RSM). Associated with the B/C, C/H, and P parameters, BDD's diamond crystallite structure, graphite-sp2 C, and grain size influenced the performance of the fabricated BDD electrodes. At 0.125 A cm−2 and 25 °C, the pseudo-first order reaction rate constants of the GGE and TOC removals were 0.33 and 0.031 min−1, respectively, and such removals were better in 0.5 M Na2SO4 than in real hospital wastewater. Both direct and indirect oxidation of GGE occurred during electrolysis. Solution pH affected the indirect oxidation of GGE by •OH, SO4•−, or persulfate electrochemically generated during electrolysis. Several intermediates, including guaiacol, quinones, (aromatic and aliphatic) acids, and hexane-2,5-dione were detected and used to picture the GGE degradation pathways.

Enhanced Ofloxacin Degradation Efficiency on Porous CeTi2O6 Photocatalyst - CTAB Induced Porosity

Background: Photocatalytic oxidation of organic pollutants in the environment is being studied for more than half a century. Titanate has the activity on the degradation of organic pollutants under UV light illumination. Template directed sol-gel method is capable of producing porous structure in titanate during high temperature thermal treatment. Methods: The materials were characterized using X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, surface area and pore size analyses, UV-Visible spectrometry, and Xray photoelectron spectroscopy. Photocatalytic activity of the CeTi2O6 material was evaluated through ofloxacin degradation. Results: Brannerite structured CeTi2O6 was the major component in the samples, and the addition of CTAB caused a slight growth of CeTi2O6 crystals. Porous structure formed in the porous sample after the removal of CTAB template, and the surface area and pore volume were greatly enlarged. The first order reaction rate constant for photocatalytic degradation of ofloxacin was 9.60×10-3 min-1 on the nonporous CeTi2O6 sample, and it was as large as 2.44×10-2 min-1 on the porous CeTi2O6 sample. The addition of CTAB can influence the physico-chemical properties of the porous CeTi2O6, such as the improved activity on photocatalytic degradation of ofloxacin. Conclusion: The CeTi2O6 samples composed of majority brannerite CeTi2O6, and CeTi2O6 crystallite sizes for the nonporous and porous samples were 38.1 and 43.2 nm. The burning up of CTAB during calcination produced abundant pores in the porous material. After 50 min of reaction, photocatalytic degradation efficiencies on the nonporous and porous CeTi2O6 samples were 38.1% and 70.5%.