Ti/RuO2-IrO2-SnO2 Anode for Electrochemical Degradation of Pollutants in Pharmaceutical Wastewater: Optimization and Degradation Performances

Electrooxidation of amoxicillin in aqueous solution with graphite electrodes: Optimization of degradation and deciphering of byproducts using HRMS

Contaminants of emerging concern (CECs) such as antibiotics have become a matter of worry in aquatic environments worldwide. Their presence in the environment has been increasing due to the inability of conventional wastewater and water treatments to annihilate them. Hence, attempts have been made to remove CECs using electrochemical oxidation (EO). Present study employed the low cost, active carbon based graphite sheet electrodes as anode and cathode to oxidize and degrade Amoxicillin (AMOX)- a β-lactum thiazolidine antibiotic. Optimization studies found pH 9, 45 mA cm-2, 81 cm2 electrode surface area, 6 mM electrolyte concentration and 60 min treatment time to be optimal for AMOX removal. Studies with varying concentrations of AMOX (20 mg L-1, 30 mg L-1 and 40 mg L-1) found that increase in concentrations of AMOX require higher current densities and treatment time for better TOC removal. High performance liquid chromatography photo diode array (HPLC-PDA) studies found 94% removal for 40 mg L-1 of AMOX at optimal conditions with 90% COD and 46% TOC removal. High resolution mass spectrometry (HRMS) studies using Ultra performance liquid chromatography-quadrupole time of flight-mass spectrometry (UPLC-Q-ToF-MS) identified major degradation mechanisms to be hydroxylation, β-lactum ring cleavage, breakage of thiazolidine ring chain from the aromatic ring and piperazinyl ring formation. The final byproducts of AMOX oxidation were carboxylic acids.

Sustainable application of electrocatalytic and photo-electrocatalytic oxidation systems for water and wastewater treatment: a review

Wastewater treatment and reuse have risen as a solution to the water crisis plaguing the world. Global warming-induced climate change, population explosion and fast depletion of groundwater resources are going to exacerbate the present global water problems for the forthcoming future. In this scenario, advanced electrochemical oxidation process (EAOP) utilising electrocatalytic (EC) and photoelectrocatalytic (PEC) technologies have caught hold of the interest of the scientific community. The interest stems from the global water management plans to scale down centralised water and wastewater treatment systems to decentralised and semicentralised treatment systems for better usage efficiency and less resource wastage. In an age of rising water pollution caused by contaminants of emerging concern (CECs), EC and PEC systems were found to be capable of optimal mineralisation of these pollutants rendering them environmentally benign. The present review treads into the conventional electrochemical treatment systems to identify their drawbacks and analyses the scope of the EC and PEC to mitigate them. Probable electrode materials, potential catalysts and optimal operational conditions for such applications were also examined. The review also discusses the possible retrospective application of EC and PEC as point-of-use and point-of-entry treatment systems during the transition from conventional centralised systems to decentralised and semi-centralised water and wastewater treatment systems.

Preparation and characterization of PMT-TiO2-NTs@NiO-C/Sn-Sb composite electrodes by a two-step pulsed electrodeposition method for the degradation of crystalline violet

To overcome the limitations imposed by Sn-Sb electrodes, the titanium foam (PMT)-TiO₂-NTs@NiO-C/Sn-Sb composite electrodes with cubic crystal structure are synthesized by introducing NiO@C nanosheet arrays interlayer on the TiO₂-NTs/PMT matrix through hydrothermal and carbonization process. Then a two-step pulsed electrodeposition method is used to prepare the Sn-Sb coating. Benefiting from the advantages of stacked 2D layer-sheet structure, the obtained electrodes exhibit enhanced stability and conductivity. Synergy of inner and outer layers fabricated by different pulse times strongly influence the electrochemical catalytic properties of the PMT-TiO₂-NTs@NiO-C/Sn-Sb (Sn-Sb) electrode. Hence, the Sn-Sb (b0.5 h + w1 h) electrode is the optimal electrode to degrade the Crystalline Violet (CV). Next, the effect of the four experimental parameters (initial CV concentration, current density, pH value and supporting electrolyte concentration) on the degradation of CV by the electrode are investigated. The degradation of the CV is more sensitive to alkaline pH, and the rapid decolorization of CV when the pH is 10. Moreover, the possible electrocatalytic degradation pathway of CV is performed using HPLC-MS. Results from the tests show that the PMT-TiO₂-NTs/NiO@C/Sn-Sb (b0.5 h + w1 h) electrode is an interesting alternative material in industrial wastewater applications.

Mechanism exploration of highly conductive Ni-metal organic frameworks/reduced graphene oxide heterostructure for electrocatalytic degradation of paracetamol: Functions of metal sites, organic ligands, and rGO basement

The highly conductive Ni-metal-organic framework/reduced graphene oxide (Ni-MOG/rGO) heterostructure shows an excellent catalytic activity through the modification of active sites, considerably enabling the electron transfer between rGO and Ni-MOF. However, the detailed mechanisms, i.e., the functions of separate metal sites and organic ligands and electron transfer orientation between Ni-MOFs and rGO, remain to be discussed. Here, the electrocatalytic mechanism of Ni-MOF/rGO was experimentally analyzed on the basis of the density functional theory. The dominant active sites of radical and nonradical generation were determined. Findings indicated that radicals (O2•- and •OH) and nonradicals (1O2 and active chlorine) contributed to paracetamol (APAP) degradation. Moreover, metal sites (Ni) were favorable to generate O2•- and partly •OH to initiate the reaction. By contrast, organic frameworks in Ni-MOF and rGO basement favored to generate •OH and nonradicals (1O2 and active chlorine). In this case, N sites (in Ni-MOF), which seized electrons from Ni sites, acted as the primary bonding bridge to accelerate the electron transfer from rGO to Ni-MOF. This study provided essential information to decipher the mechanism of Ni-MOF/rGO heterostructure applicable to the electrocatalytic system.

A comprehensive review on reactive oxygen species (ROS) in advanced oxidation processes (AOPs)

In this account, the reactive oxygen species (ROS) were comprehensively reviewed, which were based on electro-Fenton and photo-Fenton processes and correlative membrane filtration technology. Specifically, this review focuses on the fundamental principles and applications of advanced oxidation processes (AOPs) based on a series of nanomaterials, and we compare the pros and cons of each method and point out the perspective. Further, the emerging reviews regarding AOPs rarely emphasize the involved ROS and consider the convenience of radical classification and transformation mechanism, such a review is of paramount importance to be needed. Owing to the strong oxidation ability of radical (e.g., •OH, O₂^•-, and SO₄^•-) and non-radical (e.g., ¹O₂ and H₂O₂), these ROS would attack the organic contaminants of emerging concern, thus achieving the goal of environmental remediation. Hopefully, this review can offer detailed theoretical guidance for the researchers, and we believe it able to offer the frontier knowledge of AOPs for wastewater treatment plants (WWTPs).

Electrocatalytic oxidation of aromatic amine (4-aminobiphenyl): Kinetics and transformation products with mechanistic approach

Electrocatalytic oxidation (EO) of carcinogenic 4-aminobiphenyl (4-ABP) aromatic amine was performed using Ti-RuO₂ anodes. Current (I), pH, electrolysis time (t), and 4-ABP initial concentration (C_o ) were selected as EO parameters, and their effects on %4-ABP removal (R₁ ) and energy consumed (R₂ ) were studied. Experimental design, parameters optimization, and their interaction with responses R₁ and R₂ were performed using response surface methodology. At optimized parameters, %TOC removal and 4-BP mineralization current efficiency (%MCE) were assessed to evaluate the potential of Ti/RuO₂ anodes towards 4-ABP mineralization. Simultaneous TOC and 4-ABP degradation kinetics were also studied to evaluate the competition in 4-ABP mineralization and degradation. Further, UPLC-Q-TOF-MS analysis was performed to identify the 4-ABP transformation products during the EO, and a mechanism describing the EO transformation was proposed. At optimum parameters (I = 1.2 A; pH = 4.0; t = 30 min; C_o  = 30 ppm), responses were found to be R₁  = 60.25%; R₂  = 2.49 kWh/g of 4-ABP removed. %TOC removal and %MCE were 52.4% and 34.2%, respectively. PRACTITIONER POINTS: 4-Aminobiphenyl electro-oxidation (EO) was explored using Ti/RuO₂ anode. Achieved 34.2% mineralization current efficiency, 52.4% TOC and 61.3% TKN removal. Three electro-oxidation transformation products of 4-ABP were detected. 4-Aminobiphenyl was found degrading at ≈1.6 times higher rate than TOC A plausible EO transformation pathway and mechanism was proposed.

Manganese-doped molybdenum oxide boosts catalytic performance of electrocatalytic wet air oxidation at ambient temperature

Mn-doping strategy was adopted to modify the structure of MoO₂ for enhancing its catalytic activity towards room-temperature electrocatalytic wet air oxidation (ECWAO) reaction. A series of Mn-doped MoO₂ were prepared on carbon support, and their structures were investigated to elucidate the productive effect of Mn doping on the catalytic activity of MoO₂. The incorporation of Mn^III/Mn^II into the MoO₂ lattice induced the transformation from Mo^IV to Mo^V and created more oxygen vacancies. Such structural modifications promoted the electron transfer of MoO₂ through the redox couples between Mo^VI/Mo^V/Mo^IV and Mn^III/Mn^II, and facilitated the transformation from O₂ to adsorbed oxygen species on MoO₂ surface. As a result, the ECWAO catalytic activities of Mn-doped MoO₂/graphite felt (MoO₂/GF) outperformed the activity of MoO₂/GF. Among the synthesized series, Mn_0.066:MoO₂/GF exhibited the highest activity with the maximum turnover frequency (TOF) promoted by 59% than the undoped MoO₂/GF. Under the catalysis of Mn_0.066:MoO₂/GF, the ECWAO process obtains mineralization efficiencies generally above 85% in degrading typical pharmaceutics and person care products (PPCPs). These findings are anticipated to open up a new venue in the design and fabrication of highly active catalysts for air oxidation reactions by using the strategy of selective dopant-induced structure modification.

Electrochemical Degradation of Crystal Violet Using Ti/Pt/SnO2 Electrode

Today, organic wastes (paints, pigments, etc.) are considered to be a major concern for the pollution of aqueous environments. Therefore, it is essential to find new methods to solve this problem. This research was conducted to study the use of electrochemical processes to remove organic pollutants (e.g., crystal violet (CV)) from aqueous solutions. The galvanostatic electrolysis of CV by the use of Ti/Pt/SnO2 anode, were conducted in an electrochemical cell with 100 mL of solution using Na2SO4 and NaCl as supporting electrolyte, the effect of the important electrochemical parameters: current density (20–60 mA cm−2), CV concentration (10–50 mg L−1), sodium chloride concentration (0.01–0.1 g L−1) and initial pH (2 to 10) on the efficiency of the electrochemical process was evaluated and optimized. The electrochemical treatment process of CV was monitored by the UV-visible spectrometry and the chemical oxygen demand (COD). After only 120 min, in a 0.01 mol L−1 NaCl solution with a current density of 50 mA cm−2 and a pH value of 7 containing 10 mg L−1 CV, the CV removal efficiency can reach 100%, the COD removal efficiency is up to 80%. The process can therefore be considered as a suitable process for removing CV from coloured wastewater in the textile industries.