Photoelectrocatalytic Oxidation of Methyl Orange on a TiO2 Nanotubular Anode Using a Flow Cell

Photo-electrochemical oxidation flow system for stormwater herbicides removal: Operational conditions and energy consumption analysis

Photoelectrochemical oxidation (PECO) is a promising advanced technology for treating micropollutants in stormwater. However, it is important to understand its operation prior to practical validation. In this study, we introduced a flow PECO system designed to evaluate its potential for full-scale applications in herbicides degradation, providing valuable insights for future large-scale implementations. The PECO flow reactor demonstrated the ability to treat a larger volume of stormwater (675 mL, approximately 10 times more than previous batch experiments) with effective removal rates of 92 % for diuron and 22 % for atrazine over 6 h of operation at 2 V. To address the large volume issue in stormwater treatment, a multiple module parallel application design is being considered to increase the treatment capacity of the PECO flow reactor. During the flow reactor operations, flow rate was found to have a notable impact on removal performance, particularly for diuron. At a flow rate of 610 mL min-1, approximately 90 % removal of diuron was achieved, while at 29 mL min-1, the removal efficiency decreased to 60 %. While light intensity had minimal effect on diuron degradation (all settings achieved over 90 % removal), it enhanced atrazine degradation from 9 % to 31 % with an increase in intensity from 63 mW cm-2 to 144 mW cm-2. Remarkably, the PECO flow system exhibited excellent removal performance (>90 % removal) for diuron even at extremely high initial pollutant concentrations (240 μg L-1), demonstrating its capacity to handle varying contaminant loads in stormwater. Energy consumption analysis revealed that flow rate as the primary factor influenced the specific energy consumption rate. Higher flow rate (e.g., 610 mL min-1) were preferable in flow reactor due to its well-balanced performance between removal and energy consumption. These findings confirm that the PECO flow system offers an efficient and promising approach for stormwater treatment applications.

Experimental study on the optimisation of azo-dyes removal by photo-electrochemical oxidation with TiO2 nanotubes

An experimental investigation is here presented on the photo-electrochemical removal of Methyl Orange (MO), selected as a model of the organic dyes, contained in wastewaters. The process is carried out in an electrochemical flow reactor, in which titania nanotubular electrode is irradiated with a simulated solar light. Design of Experiments (DOE) technique is used to plan the experimental campaign and investigate on the single and combined effects of applied current, electrolyte flow rate, and initial MO concentration, on the specific reaction rate. The results of the DOE analysis, also combined with the study of the distribution of the intermediate products, confirm a reaction mechanism mediated by OH radicals; high applied current and low reactant concentration resulted as favourable conditions to achieve high specific reaction rate of color removal.

Study of TiO2/Ti4O7 photo-anodes inserted in an activated carbon packed bed cathode: Towards the development of 3D-type photo-electro-Fenton reactors for water treatment

In this work, commercially available Polymethyl-meta-acrylate (PMMA) spectroscopy cells were modified on the external walls with films of TiO₂, Ti₄O₇ or TiO₂/Ti₄O₇ mixtures. Film characterization was carried out using SEM and UV–vis spectroscopy. The results of photocatalytic (PC), electro-oxidation (EO), and photoelectrochemical (PEC) experiments on the decolorization of a methyl orange (MO) model dye solution showed that while anatase provides better photocatalytic properties and the partially reduced Ti₄O₇ larger electronic conductivity, the TiO₂/Ti₄O₇ composite film behaves as a semiconductor substrate that combines the advantages of both materials (for PEC experiments for instance, decolorization values for the model dye solution using TiO₂, Ti₄O₇ and a TiO₂/Ti₄O₇ mixed film, corresponded to 35%, 46% and 53%, respectively). In order to test this film as an effective photoanode material in a 3-D type reactor for water treatment processes, a TiO₂/Ti₄O₇ modified PMMA spectroscopy cell was inserted in an activated carbon (AC) bed so that the semiconductor material could be illuminated using an external UV source positioned inside the PMMA cell. The connected AC particles that were previously saturated with MO dye were used as cathode sites for the oxygen reduction reaction so that the photoelectrochemical reactions that take place in the anode could be complemented with coupled electro-Fenton processes in the cathode. As expected, the combination resulted in an effective decolorization of the dye solution that results from a complex combination of processes. The experimental decolorization data was successfully fitted to a pseudo-first order kinetic model so that a deeper understanding of the contribution of each process in the reactor could be obtained.

Reusability and photocatalytic activity of bismuth-TiO2 nanocomposites for industrial wastewater treatment

In this study, bismuth-TiO₂ nanotube (Bi-TNT) composites were used for the treatment of industrial wastewater. Bi-TNT were synthesized using two- and one-step anodization methods. The obtained composites were analyzed using X-ray diffraction, field emission scanning electron microscopy, UV-visible diffuse reflectance spectroscopy, Energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. For the two-step Bi-TNT composites, we investigated the effect of different Bi deposition times, Bi concentrations, and Bi deposition voltages on photodegradation efficiency. For the one-step Bi-TNT composites, we investigated the effect of different anodization voltages, anodization times, and Bi concentrations. Initially, the optimal synthesis conditions for two- and one-step Bi-TNT catalysts were identified and then these optimized conditions were used for industrial wastewater treatment that was collected from Banwol Sihwa Industrial Complex Republic of Korea. The Bi-TNT two- and one-step composites showed 2.0 and 2.5 times higher photocatalytic activity, respectively, for industrial wastewater treatment than that of TNT in visible-light. Recycling of Bi-TNT composites showed that the one-step composite method was more efficient and stable than the two-step method because Bi coupling and nanotube formation simultaneously occurred.

Electrochemical anodization of graphite oxide-TiO2 nanotube composite for enhanced visible light photocatalytic activity

The electrochemical anodization method was used to dope graphite oxide (GO) onto TiO₂ nanotubes (TNTs). This study focused on enhancement of the photocatalytic activity of TNTs in the visible light region. In this study, we have checked the effect of different GO concentrations and effect of GO doping time on photocatalytic efficiency of composite. The photocatalytic activity of the GO-TNT composite was tested by degradation of an organic compound. The organic compound was most severely degraded (95%) when the GO-TNT catalyst was doped at an anodization of 60 V for 13 min and GO concentration of 0.25 g L^-1. This degradation was 5.6 times higher than that of bare TiO₂. The as-prepared catalyst was characterized using FE-SEM, XRD, AES, PL, UV-Vis DRS, and Raman analysis. Recycling of the GO-TNT composite was also performed in order to examine the stability of the visible light catalyst. We observed that the doping of GO on the TNT surface can enhance the photocatalytic efficiency under visible light. Graphene acts as an electron transport; therefore, GO-TNTs were favorable for the separation of e^- and h⁺ charges. This promoted the formation of OH radicals, h⁺, and superoxides, all of which degrade organics.

Synthesis of NiFe2O4-LDH Composites with High Adsorption and Photocatalytic Activity for Methyl Orange Degradation

The presence of hazardous chemicals in wastewater produced by industrial activities and human metropoles is threating the availability of safe drinking water. The development of a multifunctional material coupling adsorption and photocatalytic activity is hereby particularly promising for the removal of pollutants. We have proved the adsorption and catalytic activity of NiFe2O4-layered double hydroxide (LDH) composite through the degradation of methyl orange (MO) at room temperature under visible light. This degradation is enhanced by using a set of small light-emitting diodes (LEDs) providing a uniform 405 nm UV light. The remediation process is based on a first-step rapid adsorption of MO molecules by the LDH structures followed by the photocatalytic oxidation of the pollutant by the (·OH) radicals produced by the NiFe2O4 semiconductor nanoparticles (NPs). The magnetic properties of the ferrite NPs allow a facile separation of the composite from the liquid media via a simple magnet. NiFe2O4-LDH composite could find wide application as a highly effective adsorbent/oxidizing catalyst operating under visible or near UV light.

Influence of the electronic structures on the heterogeneous photoelectrocatalytic performance of Ti/RuxSn1-xO2 electrodes

DSA-type Ti/Ru_xSn_1-xO₂ electrodes were prepared by thermal decomposition method as photoelectrocatalysts (PECs) and extensively characterized by various sophisticated techniques. First-principles calculations was employed to study the effects of Ru content on the electronic structures of the Ru_xSn_1-xO₂ coatings. The photoelectric-synergistic catalytic activity of the Ti/Ru_xSn_1-xO₂ electrodes was evaluated for the degradation of methyl orange (MO) in aqueous solution. The results show that the RuO₂-SnO₂ solid solution could be formed. The band gaps of the Ru_xSn_1-xO₂ coatings gradually decreased and eventually turned into metallic conductivity with the increase of ruthenium content. As a PEC electrode, reducing band gap is helpful to improve electronic conductivity and the electrocatalytic activity, but not always advantageous to increase the photocatalytic activity. Because too narrow band gap will sacrifice the photogenerated charge carriers and thus reduce photocatalytic activity of the electrode. In our experiments, the rate constant of Ti/Ru_0.05Sn_0.95O₂ electrode increased with increasing Ru content and exhibited the maximum rate for 5% Ru loading. The stability test showed the photoelectrocatalytic activity of the Ti/Ru_0.05Sn_0.95O₂ electrode almost had no attenuation after 100h photoelectrolysis, revealing that this electrode has good long-term stability.

Hierarchical TiO2 nanonetwork–porous Ti 3D hybrid photocatalysts for continuous-flow photoelectrodegradation of organic pollutants

Hierarchical TiO₂/porous Ti hybrid photocatalysts prepared by powder metallurgical porous titanium material can be act as 3D electrodes for photoelectrocatalysis. High performance continuous filtration photoelectrocatalytic device for waste water treatment has been designed and built by using UV-LED as light source.