Preparation of carbon-sensitized and Fe–Er codoped TiO2 with response surface methodology for bisphenol A photocatalytic degradation under visible-light irradiation

The carbon-sensitized and Fe–Er codoped TiO2 (Fe/Er–TiO2) was synthesized by a facile solvothermal method using titanium isopropoxide both as titanium precursor and carbon source, as well as ferric nitrate and erbium nitrate as dopants source. The response surface methodology (RSM) with central composite design (CCD) model was used to obtain the optimum synthesis conditions for this novel Fe/Er–TiO2. The RSM was also applied to study the main and interactive effects of the parameters (Er concentration [Er], Fe concentration [Fe] and calcination temperature [CT]) investigated. The experimental results indicated an improved photocatalytic activity of Fe/Er–TiO2 for bisphenol A (BPA) degradation compared to the pristine TiO2, Er–TiO2, Fe–TiO2 and Degussa P25 (P25) under visible light irradiation. In addition, the RSM model obtained (R2 = 0.929) showed a satisfactory correlation between the experimental results and predicted values of BPA removal efficiency. The identified optimum condition for preparing Fe/Er–TiO2 was 1.5 mol%, 1.25 mol% and 450 °C for [Er], [Fe] and [CT], respectively. Moreover, the photocatalytic activity of the optimized Fe/Er–TiO2 was preserved effectively even after ten cycles of use. The possible photocatalytic mechanisms induced by the Fe/Er–TiO2 under visible light irradiation are proposed. The enhanced photocatalytic activity of Fe/Er–TiO2 can be attributed to the synergistic effects of photosensitizing (Csingle bondO band), narrowed band gap and enhanced e−/h+ separation (Ti–O–Fe linkage), and upconversion luminescence property (Ti–O–Er linkage)

Preparation, characterization and performance of a novel visible light responsive spherical activated carbon-supported and Er3+:YFeO3-doped TiO2 photocatalyst

A novel spherical activated carbon (SAC) supported and Er3+:YFeO3-doped TiO2 visible-light responsive photocatalyst (Er3+:YFeO3/TiO2-SAC) was synthesized by a modified sol–gel method with ultrasonic dispersion. It was characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), powder X-ray diffractometer (XRD) and UV–vis diffuse reflectance spectrophotometer (DRS). The photocatalytic activity of Er3+:YFeO3/TiO2-SAC was evaluated for degradation of methyl orange (MO) under visible light irradiation. The effects of calcination temperature and irradiation time on its photocatalytic activity were examined. The experimental results indicated that Er3+:YFeO3 could function as an upconversion luminescence agent, enabling photocatalytic degradation of MO by TiO2 under visible light. The Er3+:YFeO3/TiO2 calcinated at 700 °C showed the highest photocatalytic capability compared to those calcinated at other temperatures. The photocatalytic degradation of MO followed the Langmuir–Hinshelwood kinetic model. Although the photocatalyst showed a good physical stability and could tolerate a shear force up to 25 × 10−3 N/g, its photocatalytic activity decreased over a four-cycle of reuse in concentrated MO solution, indicating that the decreased activity was ascribed to the fouling of catalyst surface by MO during the degradation process. However, the fouled Er3+:YFeO3/TiO2-SAC could be regenerated through water rinsing-calcination or acid rinsing-calcination treatment

Active H₂ Harvesting Prevents Methanogenesis in Microbial Electrolysis Cells

Undesired H₂ sinks, including methanogenesis, are a serious issue faced by microbial electrolysis cells (MECs) for high-rate H₂ production. Different from current top-down approaches to methanogenesis inhibition that showed limited success, this study found active harvesting can eliminate the source (H₂) from all H₂ consumption mechanisms via rapid H₂ extraction using a gas-permeable hydrophobic membrane and vacuum. Active harvesting completely prevented CH₄ production and led to H₂ yields (2.62–3.39 mol of H₂/mol of acetate) much higher than that of the control using traditional spontaneous release (0.79 mol of H₂/mol of acetate). In addition, existing CH₄ production in the control MEC was stopped once the switch to active H₂ harvesting was made. Active harvesting also increased current density by 36%, which increased operation efficiency and facilitated organic removal. Energy quantification shows the process was energy-positive, as the H₂ energy produced via active harvesting was 220 ± 10% of external energy consumption, and a high purity of H₂ can be obtained

Nickel-Based Membrane Electrodes Enable High-Rate Electrochemical Ammonia Recovery

Wastewater contains significant amounts of nitrogen that can be recovered and valorized as fertilizers and chemicals. This study presents a new membrane electrode coupled with microbial electrolysis that demonstrates very efficient ammonia recovery from synthetic centrate. The process utilizes the electrical potential across electrodes to drive NH₄⁺ ions toward the hydrophilic nickel top layer on a gas-stripping membrane cathode, which takes advantage of surface pH increase to realize spontaneous NH₃ production and separation. Compared with a control configuration with conventionally separated electrode and hydrophobic membrane, the integrated membrane electrode showed 40% higher NH₃–N recovery rate (36.2 ± 1.2 gNH₃–N/m²/d) and 11% higher current density. The energy consumption was 1.61 ± 0.03 kWh/kgNH₃–N, which was 20% lower than the control and 70–90% more efficient than competing electrochemical nitrogen recovery processes (5–12 kWh/kgNH₃–N). Besides, the negative potential on membrane electrode repelled negatively charged organics and microbes thus reduced fouling. In addition to describing the system’s performance, we explored the underlying mechanisms governing the reactions, which confirmed the viability of this process for efficient wastewater–ammonia recovery. Furthermore, the nickel-based membrane electrode showed excellent water entry pressure (∼41 kPa) without leakage, which was much higher than that of PTFE/PDMS-based cathodes (∼1.8 kPa). The membrane electrode also showed superb flexibility (180° bend) and can be easily fabricated at low cost (<20 $/m²)

The Microbial Electrochemical Current Accelerates Urea Hydrolysis for Recovery of Nutrients from Source-Separated Urine

This study demonstrates that a wastewater-driven microbial electrochemical process greatly facilitates traditional rate-limiting urea hydrolysis and efficiently recovers ammonium and phosphate nutrients from source-separated urine. Using both synthetic and diluted actual urine and wastewater, 76–87% of nitrogen and 72–93% of phosphorus were continuously removed from source-separated urine and collected in recovery solutions. The acceleration of hydrolysis and nutrient recovery were driven by the electrical potential generated during wastewater treatment. The efficient nutrient recovery is attributed to the increase in the rate of hydrolysis induced by continuous ammonium migration and removal, which alleviates storage, health, and operational issues associated with the utilization of urine. Further investigations of removal behaviors of micropollutants under electrochemical conditions will be performed

Electrochemical Control of Redox Potential Arrests Methanogenesis and Regulates Products in Mixed Culture Electro-Fermentation

This study demonstrates the feasibility of using solid electrodes as an alternative source or sink of electrons to regulate the redox potential of mixed culture anaerobic reactors, so tunable fermentation products can be generated. The product spectrum was characterized under the working potentials of −1.0, −0.6, and −0.2 V (versus Ag/AgCl), which spans the electron flow direction from cathodic current to anodic current. Results show that in neutral pH a more negative working potential led to higher production of CH₄, H₂, and acetic acid, while increasing the potential from −1.0 to −0.2 V (versus Ag/AgCl) greatly reduced methanogenesis by 68% and acetic acid generation by 33%. Lowering initial pH to 6.2 reduced such effects by electrical potential. The decrease of working potential slightly decreased butyric acid production and showed little impact on propionic acid under both pH conditions. When the reactor switched from poised conditions to open circuit condition, more propionic acid and acetic acid while less butyric acid production was observed. This redox-potential-based control presents a new approach to regulate the mixed culture fermentation and improve product tunability