Process Optimization of Electrochemical Treatment of COD and Total Nitrogen Containing Wastewater

In this work, an electrochemical method for chemical oxygen demand (COD) and total nitrogen (TN, including ammonia, nitrate, and nitrite) removal from wastewater using a divided electrolysis cell was developed, and its process optimization was investigated. This process could effectively relieve the common issue of NO3−/NO2− over-reduction or NH4+ over-oxidation by combining cathodic NO3−/NO2− reduction with anodic COD/NH4+ oxidation. The activity and selectivity performances toward pollutant removal of the electrode materials were investigated by electrochemical measurements and constant potential electrolysis, suggesting that Ti electrode exhibited the best NO3−/NO2− reduction and N2 production efficiencies. In-situ Fourier transform infrared spectroscopy was used to study the in-situ electrochemical information of pollutants conversion on electrode surfaces and propose their reaction pathways. The effects of main operating parameters (i.e., initial pH value, Cl− concentration, and current density) on the removal efficiencies of COD and TN were studied. Under optimal conditions, COD and TN removal efficiencies from simulated wastewater reached 92.7% and 82.0%, respectively. Additionally, reaction kinetics were investigated to describe the COD and TN removal. Results indicated that COD removal followed pseudo-first-order model; meanwhile, TN removal followed zero-order kinetics with a presence of NH4+ and then followed pseudo-first-order kinetics when NH4+ was completely removed. For actual pharmaceutical wastewater treatment, 79.1% COD and 87.0% TN were removed after 120 min electrolysis; and no NH4+ or NO2− was detected.

Elucidation of the Nucleophilic Potential of Diazocyclopentadiene

Diazocyclopentadiene reacts with benzhydrylium ions (Ar2CH+) to give 2,5-dibenzhydryl-substituted diazocyclopentadienes. The kinetics have been determined photometrically in dichloromethane under pseudo-first-order conditions using diazocyclopentadiene in excess. Plots of the second-order rate constants (log k 2) versus the electrophilicity parameters E of the benzhydrylium ions gave the nucleo­philicity parameter N = 4.84 and susceptibility s N = 1.06 for diazo­cyclopentadiene according to the correlation log k(20 °C) = s N(E + N). Diazocyclopentadiene thus has a similar nucleophilic reactivity as pyrrole. Previously reported electrophilic substitutions of diazocyclopentadiene are rationalized by these parameters and new reaction possibilities are predicted.

Chemical effects induced by gas–liquid jet flow

The gas-liquid jet flow was proved to be capable of inducing chemical consequences which can lead to the decomposition of methylene blue (MB). The reaction process follows a pseudo-first-order kinetics....

Penyisihan Kontaminan dari Air Limbah Hasil Daur Ulang Baterai LiFePO4 (LFP) Menggunakan Penukar Ion Resin Kation Amberlite HPR1100 Na dan Resin Anion Dowex Marathon A

Pada tahun 2025, diperkirakan kebutuhan baterai Li-ion akan mencapai 400.000 ton. Upaya strategis diperlukan untuk mewujudkan pemakaian baterai Li-ion yang berkelanjutan. Setelah siklus pemakaian baterai Li-ion berakhir, baterai Li-ion akan diproses kembali untuk diambil kandungan logam-logam penting yang terkandung di dalam katoda, terutama litium. Secara umum, proses recycle tersebut dilakukan dengan metode hidrometalurgi yang terdiri atas rangkaian leaching dan presipitasi. Namun demikian, dalam proses pemurnian tersebut dihasilkan air limbah yang mengandung beragam logam dengan konsentrasi yang berbeda. Untuk baterai LFP, logam-logam tersebut berasal dari katoda yang mengandung Li, Na, Si, dan PO4. Proses pelindian dan pencucian serbuk katoda membutuhkan air dalam jumlah yang relatif besar. Pengolahan air limbah hasil proses daur ulang baterai diharapkan dapat secara signifikan meningkatkan efisiensi penggunaan air. Pada eksperimen ini, metode adsorpsi batch dengan ion-exchange resin kation Amberlite HPR1100 Na dan resin anion Dowex Marathon A digunakan untuk menghilangkan ion logam dari air limbah artifisial. Pengambilan sampel air limbah yang diolah diambil pada menit ke-3, 6, 10, 20, 30 dan hari ke-3. Berdasarkan pada hasil removal percentage, diperoleh bahwa pengolahan air limbah artifisial metode adsorpsi dengan menggunakan ion-exchange resin kation Amberlite HPR1100 Na dapat mengurangi kadar ion litium dan natrium sampai 100% pada menit ke-20 dengan variasi dosis adsorben 10 g/100 mL, sedangkan penggunaan ion-exchange resin anion Dowex Marathon A dapat mengurangi kadar ion fosfat sampai 100% pada menit ke-30 dengan dosis adsorben 10 g/100 mL. Dengan adsorpsi isotherm didapat model Langmuir lebih sesuai dengan data eksperimen dengan nilai parameter Qm dan KL untuk ion litium sebesar 1,16 mg/g dan 2,57 mg/g, ion natrium sebesar 74,62 mg/g dan 0,04 mg/gL/mg, dan ion fosfat sebesar 208,33 mg/g dan 0,06 mg/g. Selain itu, studi kinetika menunjukkan bahwa model pseudo second-order memiliki kesesuaian data yang lebih baik daripada pseudo first-order.

Adsorption Kinetics of NO2 Gas on Pt/Cr-TiO2/Pt-Based Sensors

Metal oxides are excellent candidates for the detection of various gases; however, the issues such as the limited operating temperature and selectivity are the most important ones requiring the comprehensive understanding of gas adsorption kinetics on the sensing layer surfaces. To this context, the present study focuses mainly on the fabrication of a Pt/Cr-TiO2/Pt type sensor structure that is highly suitable in reducing the operating temperature (from 400 to 200 °C), extending the lower limit NO2 gas concentration (below 10 ppm) with fast response (37 s) and recovery (24 s) times. This illustrates that the sensor performance is not only solely dependent on the nature of sensing material, but also, it is significantly enhanced by using such a new kind of electrode geometry. Moreover, Cr doping into TiO2 culminates in altering the sensor response from n- to p-type and thus contributes to sensor performance enhancement by detecting low NO2 concentrations selectively at reduced operating temperatures. In addition, the NO2 surface adsorption kinetics are studied by fitting the obtained sensor response curves with Elovich, inter-particle diffusion, and pseudo first-order and pseudo second-order adsorption models. It is found that a pseudo first-order reaction model describes the best NO2 adsorption kinetics toward 7–170 ppm NO2 gas at 200 °C. Finally, the sensing mechanism is discussed on the basis of the obtained results.

Adsorption of Chromium (VI) by Cu (I)-MOF in Water: Optimization, Kinetics, and Thermodynamics

To investigate the adsorption behavior of Cu (I)-MOF material for chromium (VI) in water, the parameters of influencing adsorption were optimized and found as follows: the optimal pH was 6 for the adsorption of Cr (VI) by the Cu (I)-MOF, the optimal amount of adsorbent was 0.45 g·L−1, and the adsorption saturation time was within 180 min. Subsequently, the kinetics results were fitted by four models such as pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. Among them, the adsorption of chromium (VI) was more inclined to the pseudo-first-order model (Radj2 = 0.9230). Then, the isotherm data were fitted by Langmuir and Freundlich models. The results indicated that Langmuir isotherm was the excellent match model (Radj2 = 0.9827). It belongs to a monolayer adsorption, and the maximum adsorption capacity was 95.92 mg·g−1. Subsequently, the thermodynamic parameters of the adsorption were calculated as follows: enthalpy change (ΔHθ) was −8.583 kJ·mol−1, entropy change (ΔSθ) was −8.243 J·mol−1 K−1, and the Gibbs function change (ΔGθ) was less than zero in the temperature range of 288–328 K, indicating that the reaction was spontaneous. Finally, both the spectra of infrared and XPS supported the adsorption mechanism that belonged the ion exchange. The spectra of XRD and SEM images shown that the structure of Cu (I)-MOF remained stable for at least 3 cycles. In conclusion, Cu (I)-MOF material has a high adsorption capacity, good water stability, low cost, and easy to prepare in large quantities in practical application. It will be a promising adsorbent for the removal of Cr (VI) from water.

A Novel Spectrophotometric Determination and Kinetic Study of Sulfamethoxazole in Pure and Tablet Formulation using 9-chloroacridine Reagent

A spectrophotometric method has been developed for analysis of Sulfamethoxazole (SMX) in pure and dosage forms. The method is based on the reaction of the SMX with 9-chloroacridine (9-CA) reagent in organic and acidic medium, to produce a yellow product having maximum absorption at 448 nm. Beer’s law was obeyed in the concentration range 1-30 μg.ml-1 with molar absorptivity of 1.63x104 L.mol-1.cm-1 with good detection and quantification limits. Accuracy (Average recovery %) and precision are 98.43% and 0.651, respectively. The proposed method was applied successfully for determination of Sulfamethoxazole in its commercial dosage form as tablet and agree well with the official method. The equilibrium constant and the thermodynamic functions (ΔHo, ΔGº and ΔSº) of the complex formation were estimated. The study revealed that the complex formation could occur spontaneously, the type of interacting forces between SMX and 9-CA are physical is nature and association increases the order of the studied systems. The results of kinetic parameters indicated that, the reaction is pseudo first order with respect to SMX. The rate constant at various temperatures and the thermodynamic functions of activation were determined. Theoretical parameters were calculated by applying the semi-empirical Austin method (AM1). These parameters are helped to suggest reaction mechanism and supporting other results.

Study of Adsorption Properties of Bentonite Clay

The clay used in this study was the bentonite from Mostagnem, Algeria. This material is used in many fields such as drilling, foundry, painting, ceramics, etc. It can also be applied in the treatment of wastewaters from chemical industries by means of adsorption. In this chapter the physicochemical properties of bentonite were determined by using several analyses techniques such as chemical composition, XRD, FTIR and SBET. The bentonite was intercalated by aluminum poly-cations solution and cethytrimethyl ammonium bromide. The acid activation of natural bentonite was performed by treatment with hydrochloric acid at different concentrations. The surface water pollutants removed by the modified bentonites are bemacid yellow E-4G and reactive MX-4R dyes, and fungicide chlorothalinil. The Langmuir and Freundlich adsorption models were applied to describe the related isotherms. The pseudo-first order and pseudo-second order kinetic models were used to describe the kinetic data. The changes of enthalpy, entropy and Gibbs free energy of adsorption process were also calculated.

Comparative study on photooxidation of methyl orange using various UV/oxidant systems

In the present work, a comparative study of the photooxidation of an aqueous solution of Methyl Orange (MeO) has been realized using H2O2 and IO3 −, BrO3 −, ClO3 −, ClO4 −, BO3 − ions in the presence of UV low pressure mercury lamp (UV-C light at λ max = 254 nm). The initial concentration of MeO in all experiments was 6 × 10−5 mol L−1. The degradation rate of MeO follows pseudo-first-order kinetics in all UV/Oxidant systems. The highest degradation rate of MeO was in the BrO3 −/UV254nm system. Different systems were compared for an oxidant concentration of 10−2 mol L−1 and the obtained results showed that decolorization followed the decreasing order: BrO 3 − /UV 254 nm > IO 3 − /UV 254 nm > H 2 O 2 /UV 254 nm > BO 3 − /UV 254 nm > ClO 3 − /UV 254 nm = ClO 4 − /UV 254 nm = UV 254 nm . The optimization of oxidants concentration for each process was determined (10−2 mol L−1 for IO3 − which gives almost the same k app for 5 × 10−3, 10−2 mol L−1 for BO3 − and 5 × 10−2 mol L−1 for H2O2). No degradation of MeO in presence of ClO3 − and ClO4 − because these ions do not absorb at 254 nm, therefore they do not generate radical species which degrade organic pollutants. The mineralization was also studied where it was reached 97% after 5 h of irradiation for both H2O2/UV254 nm and BO3 −/UV254 nm systems.

Application of polymer-coated Macadamia integrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation

Freely suspended and porous basket restrained granules of palladium nanoparticles supported on polymer-grafted Macadamia nutshell biomass (Pd@Polym-MNS) composite were used for the treatment chromium(VI)-containing water. In the presence of formic acid, the Pd@Polym-MNS demonstrated its activity in the adsorption-reduction-based conversion of noxious chromium(VI) to less toxic chromium(III) with a low activation energy of 13.4 kJ mol–1, ΔH0 (+ 10.8 kJ mol–1), ΔS0 (−270.0 J mol–1 K–1), and ΔG0 (+ 91.3 to + 98.0 kJ mol–1) indicated the exothermic, endergonic and non-spontaneous nature of the catalytic redox reaction. In addition to facilitating easy recovery, rinsing, and reuse, restraining the Pd@Polym-MNS in the basket reactor helped maintain the integrity of the catalysts by preventing violent collisions of suspended granules with the mixing apparatus and the walls of the reaction vessel. Whereas the pseudo-first-order rate constant was recorded as 0.157 min–1 upon initial use, values of the mean and relative standard deviation for the second, third and fourth consecutive uses were found to be 0.219 min–1 and 1.3%, respectively. According to a response surface methodological approach to batch experimentation, the initial concentration of chromium(VI) and catalyst dosage had the greatest impact on the redox reaction rate, accounting for 85.7% and 11.6% of the variability in the value of the pseudo-first-order rate constant, respectively. Mutually beneficial effects of the combinations of high formic acid and low chromium(VI) concentration, high temperature and catalyst dosage as well as high formic acid and catalyst dosage were recorded.