A biochar (BC) harbored Ag₃PO₄/α-Fe₂O₃ type-Ⅰ heterojunction (Ag-Fe-BC) was prepared by a hydrothermal-impregnation method to transfer active center of heterojunctions. The electrochemical and spectroscopic tests demonstrated that BC enhanced the catalytic performance of the heterojunction by enhancing photocurrent, reducing fluorescence intensity, and facilitating separation of electron-hole pairs. The photocatalytic activity showed the Ag-Fe-BC (5:1:3) could degrade Rhodamine B (20 mg/L) by up to 92.7%, which was 3.35 times higher than Ag₃PO₄/α-Fe₂O₃. Tetracycline and ciprofloxacin (20 mg/L) were degraded efficiently by 58.3% and 79.4% within 2 h, respectively. Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species (ROS) consisted of singlet oxygen (¹O₂) and superoxide (·O₂⁻). Excellent RhB adsorption and electrons capturing capacity of BC facilitated electron-hole pairs separation and ROS transferring to target organics followed by elevated degradation. Thus, a facile method was proposed to synthesize a highly efficient visible-light responsive photocatalyst for degradation of various organics in water.

In this study, we firstly used alginate to enhance an electrokinetic technology to remediate soil contaminated with divalent heavy metals (Pb²⁺, Cu²⁺, Zn²⁺). The mechanisms of alginate-associated migration of metal ions in electric field were confirmed. Alginate resulted in a high electrical current during electrokinetic process, and soil conductivity also increased after remediation. Obvious changes in both electroosmotic flow and soil pH were observed. Moreover, these factors were affected by increasing alginate dosage. The highest Cu (95.82%) and Zn (97.33%) removal efficiencies were obtained by introducing 1 wt% alginate. Alginate can desorb Cu²⁺ and Zn²⁺ ions from soil by forming unstable gels, which could be dissociated through electrolysis. However, Pb²⁺ ions did not easily migrate out of the contaminated soil. The density functional theory (DFT) calculations show Pb²⁺ ions could form a more stable coordination sphere in metal complexes than Cu²⁺ and Zn²⁺ ions. The metal removal efficiency was decreased by increasing alginate dosage at a high level. More alginate could provide more carboxyl ligands for divalent metal ions to stabilize gels, which were difficult to dissociate by electrolysis. In summary, the results indicate it is potential for introducing alginate into an electrokinetic system to remediate Cu- and Zn- contaminated soil.

The most promising technique for directly converting solar energy into clean fuels and environmental remediation by organic dye degradation is photoelectrochemical (PEC) process. We introduced Sn⁴⁺/Ti⁴⁺ doped α-Fe₂O₃@CuₓO heterojunction photoanode with complete optimization for PEC hydrogen (H₂) generation and organic dye degradation. Improvement of photocurrent photo and reducing overpotentials under optimized conditions lead to enhancing PEC performances, degradation efficiency of organic compounds, and H₂ generation generation rate. The optimized heterojunction photoanode (5TiFe@CuₓO-D) showed IPCE exceeding 42% compared with pristine hematite (Fe₀.₀₁–800₆ₕ) nanostructures (28%). Additionally, all the optimized photoanodes showed higher PEC stability for 10 h. Time-resolved PL spectra confirm the improved average lifetime for heterojunction photoanodes, supporting the enhanced PEC performance. Optimized 5TiFe@CuₓO-D material achieved PEC H₂ generation of ∼300 μL h⁻¹.cm⁻² which is two times higher than pristine hematite’s activity (150 μL h⁻¹.cm⁻²) and almost 99% degradation efficiency within 120 min of irradiation time. Therefore, a state-of-the-art study has been explored for hematite-based heterojunction photoanodes reflecting the superior PEC performance and hydrogen, methyl orange (MO) dye degradation activities. The improved results were reported because of stable morphology and better crystallinity acquired through systematic investigation of thermal effects and hydrothermal duration, improved electrical properties by Sn/Ti doping into the lattice of α-Fe₂O₃ and optimization of CuₓO deposition methods. The formation of well-defined heterojunction minimizes the recombination of the charge carrier and leads to effective transportation of excited electrons for the enhanced PEC performance.

In this work, the novel technology was used to remove heavy metal from sludge. The coupled with biodegradable ethylenediamine disuccinic acid (EDDS) and approaching anode electrokinetic (AA-EK) technique was used to enhance heavy metal removing from sludge. Electric current, sludge and electrolyte characteristics, heavy metal removal efficiency and residual content distribution, and heavy metal fractions percentage of variation were evaluated during the electrokinetic remediation process. Results demonstrated that the coupled with EDDS and AA-EK technique obtain a predominant heavy metal removal efficiency, and promote electric current increasing during the enhanced electrokinetic remediation process. The catholyte electrical conductivity was higher than the anolyte, and electrical conductivity of near the cathode sludge achieved a higher value than anode sludge during the coupled with EDDS and AA-EK remediation process. AA-EK technique can produce a great number of H⁺, which caused the sludge acidification and pH decrease. Cu, Zn, Cr, Pb, Ni and Mn obtain the highest extraction efficiency after the coupled with EDDS and AA-EK remediation, which were 52.2 ± 2.57%, 56.8 ± 3.62%, 60.4 ± 3.62%, 47.2 ± 2.35%, 53.0 ± 3.48%, 54.2 ± 3.43%, respectively. Also, heavy metal fractions analysis demonstrated that the oxidizable fraction percentage decreased slowly after the coupled with EDDS and AA-EK remediation.

During the cation exchange membrane (CEM) enhanced electrokinetic (EK) soil remediation, the nearer to the anode, the higher are the H+ concentrations and the redox potentials. As both low pH and high redox potential are helpful to speedup Cd electro-migration, soils near the anode can be quickly remedied. Usually EK process is operated with one fixed anode (FA). A novel CEM enhanced EK method with approaching anodes (AAs) is proposed to accelerate electro-migration effect. Several mesh Ti/Ru anodes were inserted as AAs in the treated soil. They were switched in turn from the anode towards the cathode. Thus high H+ ions concentrations and high redox potentials quickly migrate to the cathode. Consequently, soil remediation is accelerated and nearly 44% of energy and 40% of time can be saved. The mechanism of Cd electro-migration behavior in soils during CEM enhanced EK is described as the elution in an electrokinetically driven chromatogram. During electrokinetic remediation, the nearer to the anode, the higher are the Cd removal velocities. A novel method with approaching anodes is proposed to accelerate remediation effect.

Domestic wastewater is an important alternative source of water in the face of a growing discrepancy between water availability and demand. The use of techniques that enable the urban reuse of treated sewage is essential to make cities more sustainable and resilient to water scarcity. The main goal of this study was to evaluate the performance of an electrocoagulation-flotation system in the treatment of domestic wastewater for urban reuse. The study was performed using raw domestic wastewater samples. The electrocoagulation-flotation system was a cylindrical reactor with aluminum electrodes. The treatment conditions involved agitation at 262.5 rpm, electrical current of 1.65 A, electrolysis time of 25 min, an initial pH of 6, and inter-electrode distance of 1 cm. Overall, the electrocoagulation-flotation system was highly efficient for removal of apparent color (97.9%), chemical oxygen demand (82.9%), turbidity (95.8%), and orthophosphate phosphorous (> 98.2%). The electrocoagulation-flotation system had a consumption of electrical energy ranging from 9.5 to 13.3 kWh m⁻³, electrode mass from 294.7 to 557.0 g m⁻³, and hydrochloric acid from 4.3 to 6.6 L m⁻³. Sludge production in the system ranged from 1,125.7 to 1,835.7 g m⁻³. Treated wastewater had a satisfactory quality for several urban reuse activities. The electrocoagulation-flotation system showed potential to be used for domestic wastewater treatment for urban reuse purposes.

In this work, a cylindrical flow-through electro-Fenton reactor containing graphite felt electrodes and an Fe(II) loaded resin was evaluated for the production of the Fenton reaction mixture and for the degradation of amoxicillin (AMX) and fecal coliforms containing aqueous solutions. First, the influence of several factors such as treatment time, current intensity, flow rate, and electrode position was investigated for the electrogeneration of H₂O₂ and the energetic consumption by means of a factorial design methodology using a 2⁴ factorial matrix. Electric current and treatment time were found to be the pivotal parameters influencing the H₂O₂ production with contributions of 40.2 and 26.9%, respectively. The flow rate had low influence on the responses; however, 500 mL min⁻¹ (with an average residence time of 1.09 min obtained in the residence time distribution analysis) allowed to obtain a better performance due to the high mass transport to and from the electrodes. As expected, polarization was also found to play an important role, since for the cathode-to-anode flow direction, lower H₂O₂ concentrations were observed when compared with the anode-to-cathode flow arrangement, indicating that part of the H₂O₂ produced in the cathode was destroyed at the anode. A fluorescence study of hydroxyl radical production, on the other hand, showed that higher yields were obtained using an anode-to-cathode flow direction (up to 3.88 µM), when compared with experiments carried out using a cathode-to-anode flow path (3.11 µM). The removal of a commercial formulation of the antibiotic AMX was evaluated in terms of total organic carbon, achieving up to 57.9% and 38.63% of pollutant mineralization using synthetic and real sanitary wastewater spiked, respectively. Finally, the efficiency of the process on the inactivation of fecal coliforms in sanitary wastewater samples was assessed, reducing 90% of the bacteria after 5 min of electrolysis.

The textile industry stands out as one of the largest consumers of water among the industrial sectors. Additionally, its effluent presents characteristics such as high load of chemical oxygen demand (COD), total organic carbon (TOC), suspended solids, color, turbidity, phenol, and salts, which require an efficient treatment of the wastewater produced. Among the several researches that have arisen focused on the treatment of textile effluents, electrocoagulation stands out. This method consists of an electrochemical process that generates its own coagulant by applying electric current to metal electrodes immersed in the solution. The electrodes used in the present study are metallic plates made of scrap iron. The objective of this work is to evaluate their application in an electrocoagulation process for the decolorization of real and synthetic effluents. The efficiency of the treatment was evaluated by applying it to a synthetic effluent containing commercial indigo blue dye and to a real effluent from the textile industry, assessing parameters such as color, turbidity, pH, electrical conductivity, COD, TOC, phenol, soluble iron, sludge generation, and electrode wear. The synthetic effluent obtained average color removal of 95%, 96% phenol, and low sludge production in 120 min of electrolysis. In the real effluent from the textile industry, an average color removal of 92%, 97% turbidity, 100% phenol, 65% TOC, and 49% COD in 90 min of electrolysis was obtained. The electrocoagulation process using scrap iron as electrodes proved to be efficient in removing the dye present in the real textile industry effluent, as well as in the synthetic effluent.

Various types of industries discharge their untreated contaminated water into the environment every year. This untreated water contains the pollutants that can negatively affect the environment and biosphere. Many methods are under practice at the moment to treat this wastewater. Among the variety of methods proposed and employed currently is the electrocoagulation (EC) method. This technique involves destabilizing the pollutants of the wastewater through the electric current flowing between the electrodes. The electrodes are mainly made of iron or aluminum. Over the past years, this technique has shown a great potential towards removal of different pollutant types from variety of wastewater. Like many other processes, the EC method is also governed and affected by various parameters such as pH, operation time, types of electrodes, and current density. It is important to keep these parameters under check and at the optimum desired value for the maximum pollutant removal. The optimum value depends upon the wastewater and the composition of the contaminants to be segregated. The present study reviews and compares the efficiency of EC with other methods in use so far. Compared to other methods, EC is shown to be energy efficient and reducing operation costs. The study also presents the challenges faced by this technique, such as electrode passivation, and the possible ways to deal with them in order to improve the overall performance effectiveness.

In this study, CaO prepared by calcination treatment from abandoned Achatina fulica shell was used as a raw material, and the floral CaO/ZnO photocatalytic composite material was prepared through co-precipitation method. SEM study showed ZnO with spindle-like petals in the range of 500–1000 nm grown on the surface of CaO carrier. The mapping image shows that the base component of the floral structure is mainly CaO, which is because CaO is not only in the reaction as a carrier, but also creates an alkaline environment in the methanol system, which is advantageous for co-precipitation. UV-vis spectroscopy shows that the visible light absorption of composites has red shifts; besides, PL, EIS, and photocurrent test showed that the composites have stronger electronic hole separation capabilities. The visible light degradation test of rhodamine B showed that CaO/ZnO photocatalytic composite could degrade 90% of the pollutants in 25 min, superior to CaO and ZnO, exhibiting recyclability properties, which is a potential candidate with cost-effective and sustainable photocatalysts.