Photocatalytic Suspensions Research Articles

Photocatalytic activation of sodium percarbonate by C3N5/C2N3 homojunction for rapid water purification: Efficient electron transfer of built-in electric field

The sodium percarbonate (SPC) activation by photogenerated electron from metal-free semiconductors is a potential advanced oxidation process in water treatment. C2N3, a novel CxNy material, was used to construct a nonmetallic homojunction catalyst via loading C3N5. The C3N5/C2N3 homojunction catalyst was used to photocatalytic activate SPC to degrade acetaminophen (AP), sulfamethoxazole, tetracycline, oxytetracycline and acyclovir. The CN-2/SPC/Vis system can completely remove AP within 20 min at 15 °C, and achieve excellent removal rate in a wide pH range. Its reaction rate constant was 24 times higher than that of C3N5/C3N4/SPC/Vis system. The CN-2/SPC/Vis system showed outstanding removal efficiency in tap and lake water. Notably, CN-2 was prepared as a photocatalytic suspension sponge and exhibited superior practicability in secondary effluent simulation experiment. CN-2 sponge can completely degrade AP within 50 min. The dominant active species for AP removal were h+, •O2− and 1O2. DFT calculations and electrochemical experiments demonstrated that the built-in electric field of nonmetallic homojunction accelerated the carrier separation, and more photogenerated electrons activated SPC to generate ROS. This work provides new insights into the construction of heterojunction in photocatalytic system and reveals the application potential of homojunction in wastewater purification.

Photoelectrochemical CO2-to-fuel conversion with simultaneous plastic reforming

Solar-driven conversion of CO2 and plastics into value-added products provides a potential sustainable route towards a circular economy, but their simultaneous conversion in an integrated process is challenging. Here we introduce a versatile photoelectrochemical platform for CO2 conversion that is coupled to the reforming of plastic. The perovskite-based photocathode enables the integration of different CO2-reduction catalysts such as a molecular cobalt porphyrin, a Cu91In9 alloy and formate dehydrogenase enzyme, which produce CO, syngas and formate, respectively. The Cu27Pd73 alloy anode selectively reforms polyethylene terephthalate plastics into glycolate in alkaline solution. The overall single-light-absorber photoelectrochemical system operates with the help of an internal chemical bias and under zero applied voltage. The system performs similarly to bias-free, dual-light absorber tandems and shows about 10‒100-fold higher production rates than those of photocatalytic suspension processes. This finding demonstrates efficient photoelectrochemical CO2-to-fuel production coupled to plastic-to-chemical conversion as a promising and sustainable technology powered by sunlight. A versatile solar-driven hybrid photoelectrochemical platform has been developed for the simultaneous conversion of greenhouse gas CO2 and waste plastics into value-added fuels and chemicals with high efficiency and selectivity.

Rational Design of Carbon Nitride Photoelectrodes with High Activity Toward Organic Oxidations.

Carbon nitride (CNx ) is a light-absorber with excellent performance in photocatalytic suspension systems, but the activity of CNx photoelectrodes has remained low. Here, cyanamide-functionalized CNx (NCN CNx ) was co-deposited with ITO nanoparticles on a 1.8 Å thick alumina-coated FTO electrode. Transient absorption spectroscopy and impedance measurements support that ITO acts as a conductive binder and improves electron extraction from the NCN CNx , whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al2 O3 |ITO : NCN CNx film displays a benchmark performance for CNx -based photoanodes with an onset of -0.4 V vs a reversible hydrogen electrode (RHE), and 1.4±0.2 mA cm-2 at 1.23 V vs RHE during AM1.5G irradiation for the selective oxidation of 4-methylbenzyl alcohol. This assembly strategy will improve the exploration of CNx in fundamental and applied photoelectrochemical (PEC) studies.

Rational Design of Carbon Nitride Photoelectrodes with High Activity Toward Organic Oxidations

AbstractCarbon nitride (CNx) is a light‐absorber with excellent performance in photocatalytic suspension systems, but the activity of CNx photoelectrodes has remained low. Here, cyanamide‐functionalized CNx (NCNCNx) was co‐deposited with ITO nanoparticles on a 1.8 Å thick alumina‐coated FTO electrode. Transient absorption spectroscopy and impedance measurements support that ITO acts as a conductive binder and improves electron extraction from the NCNCNx, whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al2O3|ITO : NCNCNx film displays a benchmark performance for CNx‐based photoanodes with an onset of −0.4 V vs a reversible hydrogen electrode (RHE), and 1.4±0.2 mA cm−2 at 1.23 V vs RHE during AM1.5G irradiation for the selective oxidation of 4‐methylbenzyl alcohol. This assembly strategy will improve the exploration of CNx in fundamental and applied photoelectrochemical (PEC) studies.

Floating perovskite-BiVO4 devices for scalable solar fuel production.

Photoelectrochemical (PEC) artificial leaves hold the potential to lower the costs of sustainable solar fuel production by integrating light harvesting and catalysis within one compact device. However, current deposition techniques limit their scalability1, whereas fragile and heavy bulk materials can affect their transport and deployment. Here we demonstrate the fabrication of lightweight artificial leaves by employing thin, flexible substrates and carbonaceous protection layers. Lead halide perovskite photocathodes deposited onto indium tin oxide-coated polyethylene terephthalate achieved an activity of 4,266 µmol H2 g-1 h-1 using a platinum catalyst, whereas photocathodes with a molecular Co catalyst for CO2 reduction attained a high CO:H2 selectivity of 7.2 under lower (0.1 sun) irradiation. The corresponding lightweight perovskite-BiVO4 PEC devices showed unassisted solar-to-fuel efficiencies of 0.58% (H2) and 0.053% (CO), respectively. Their potential for scalability is demonstrated by 100 cm2 stand-alone artificial leaves, which sustained a comparable performance and stability (of approximately 24 h) to their 1.7 cm2 counterparts. Bubbles formed under operation further enabled 30-100 mg cm-2 devices to float, while lightweight reactors facilitated gas collection during outdoor testing on a river. This leaf-like PEC device bridges the gulf in weight between traditional solar fuel approaches, showcasing activities per gram comparable to those of photocatalytic suspensions and plant leaves. The presented lightweight, floating systems may enable open-water applications, thus avoiding competition with land use.

(Digital Presentation) Effects of Thermal Convection on Species Transport in Photocatalytic Suspension Reactors

Z-scheme photocatalytic suspension reactors with aqueous redox shuttles present a promising pathway for safe and low cost solar water splitting to produce hydrogen. Soluble redox shuttles act as electron relays between light absorbing particles present in the two compartments. In recent work we have demonstrated a theoretical pathway to attain up to 4% solar-to-hydrogen efficiency with passive diffusion driven species transport [1]. However, to attain larger solar-to-hydrogen efficiencies it is crucial to enhance the rate of species transport between the two reaction compartments. We report on computational and experimental investigations to explore the effects of natural convection on species transport in Z-scheme photocatalytic systems. A transient, two-dimensional fluid flow, heat- and mass-transfer model was developed for a two-compartment system with a porous separator; horizontal and vertical reactor arrangements were considered. Volumetric absorption of visible and infrared components of incident sunlight by the suspension was modeled. Transient species concentration profiles were obtained as a function of the operating solar-to-hydrogen efficiencies, porous separator morphology and the size of the compartments. Model results predict enhanced rates of transport of redox shuttle species between two compartments in the presence of thermal convection in addition to diffusion. At 10% solar-to-hydrogen efficiency, minimum redox shuttle concentration with convection decreases by 80% as compared to passive diffusion alone for a vertically stacked reaction compartment with 2 cm height. Experimental measurements have been also performed on two-compartment prototypes (horizontal and vertical) to probe the effects of natural convection on species mixing. The source of illumination was a xenon-lamp solar simulator (Newport 94023A) with an AM1.5G filter and calibrated such that the incident illumination power at the top of the reactor was 1 sun (1000 W/m2). The reactor was assembled by connecting two polycarbonate tubes (5 cm x 5 cm) with a height of 5 cm and placing a thin separator (Nafion 117 and regenerated cellulose) between the tubes to separate the compartments. A base was 3D-printed and painted black to secure the bottom compartment and maximize absorption of the incident illumination and promote natural convection. Thermocouples (K-type) were placed at various heights within the two compartments to track local temperatures within the fluid, including along the bottom surface of the lower compartment. Over a 3-hour period of 1 sun irradiance, the temperatures were recorded, and a favorable temperature gradient for natural convection was observed (ΔT ~ 2 °C) for vertically-stacked reaction compartments. The flow behavior was visualized through the injection of a colored dye at the bottom surface of the reactor and above the membrane after the 3-hour period. Image processing of the convection video is used to help quantify the rate of mixing within the compartments. Model predictions for flow behavior and temperature profiles were compared to and validated against experimental measurements. Collectively, this study implements a unique approach to predict and evaluate the effect of natural convection on species transport in Z-scheme photocatalytic reactors.[1] Bala Chandran, R., Breen, S., Shao, Y., Ardo, S., & Weber, A. Z. (2018). Evaluating particle-suspension reactor designs for Z-scheme solar water splitting via transport and kinetic modeling. Energy and Environmental Science, 11(1), 115–135. https://doi.org/10.1039/c7ee01360d Figure 1

All at once arrangement of both oxygen atoms of dioxygen into aliphatic C(sp3)-C(sp3) bonds for hydroxyketone difunctionalization

Both β- and γ- hydroxyketone structures are important units in biologically active molecules, synthetic drugs and fine chemicals. Although there are some routes available for their manufacture from pre-functionalized groups on one or two matrix molecule(s), the approaches to simply and simultaneously deposit two oxygen atoms from dioxygen into two specific C(sp3) positions of pure saturated hydrocarbons have rarely succeeded because they are involved in the targeted activation of three inert C-H σ bonds all at once. Here, we show that a TiO2-CH3CN photocatalytic suspension system enables the insertion of dioxygen into one C(sp3)-C(sp3) bond of strained cycloparaffin derivatives, by which difunctionalized hydroxyketone products are obtained in a one-pot reaction. With the cleavage event to release strain as the directional driving force, as-designed photocatalytic reaction systems show 21 examples of β-hydroxyketone products with 31%–76% isolated yields for three-membered ring derivatives and 5 examples of γ-hydroxyketone products with 30%–63% isolated yields for four-membered ring substrates. 18O isotopic labeling experiments using 18O2, Ti18O2 and intentionally added H218O, respectively, indicated that both oxygen atoms of hydroxyketone products were exclusively from dioxygen, suggesting a previously unknown H+/TiO2-e− catalyzed arrangement pathway of the hydroperoxide intermediate to convert dioxygen into hydroxyketone units.

Novel photocatalytic performance of magnetically recoverable MnFe2O4/BiVO4 for polluted antibiotics degradation

In the study, we successfully decorated MnFe2O4 on BiVO4 to highly improve its photocatalytic activity for degradation of tetracycline as well as its magnetically recovery. The decoration of MnFe2O4 on BiVO4 led to formation of MnFe2O4/BiVO4 Z scheme heterojunction to effectively prevent the charge recombination in each material. Upon visible light, the MnFe2O4/BiVO4 heterojunction produced significant available amounts of e− and h+ existing in the conduction band of the MnFe2O4 and the valence band of the BiVO4, respectively. These produced e− on the conduction band of the MnFe2O4, which reduction potential was approximately −0.41 eV, exhibited strong reduction potential reducing oxygen to produce •O2− radicals while h+ on the valence band of the BiVO4, which oxidation potential was 2.77 eV, showed strong oxidation potential oxidizing water and hydroxyl groups to produce •OH radicals. These generated active oxygen radicals effectively degraded TC in water (~92%). The used photocatalysts were easily recovered from photocatalytic suspension using an external magnet due to high magnetically activity of the MnFe2O4, which tightly bonded with BiVO4 in the MnFe2O4/BiVO4 heterojunction. Finally, the recovered MnFe2O4/BiVO4 heterojunction was very active and stable for tetracycline degradation in long-term process.

D35-TiO2 nano-crystalline film as a high performance visible-light photocatalyst towards the degradation of bis-phenol A

Dye-sensitized photocatalytic suspension system for wastewater treatment is still limited in practice due to particle aggregation, fast charge carrier recombination, poor stability and recycling issue. In this study, we combine TiO2 nano-crystalline film with D35 organic dye to fabricate a new visible-light photocatalyst D35-TiO2, which exhibits excellent visible light absorption. Its transient photocurrent is almost 10 times higher than pure TiO2 under visible light illumination (λ > 420 nm). Besides the well characterizations of the D35-TiO2 film, e.g., SEM, EDS, TEM, XRD, UV–Vis DRS, XPS, PL and I-T, degradation of bis-phenol A (BPA) is performed as the model reaction to test its photocatalytic activity. Meanwhile, we employ external bias in the reaction system to further enhance the photogenerated charge carrier separation, and improve the photocatalytic efficiency. Under the better experimental conditions of initial BPA concentration (5 mg/L), initial pH (pH 7), external bias (0.25 V) and sensitizer concentration (0.1 mM), BPA is almost completely degraded in 300 min, and the four intermediates are gradually mineralized. The ecotoxicity of BPA also decreases significantly after the photodegradation. During the reaction, O2− plays a dominant role, meanwhile ·OH and h+D35 also contribute to the BPA degradation. After five cycles, the D35-TiO2 film still maintain the normal photocatalytic activity. Due to the high stability and recyclability, the D35-TiO2 nano-crystalline film provides a sustainable way for degrading micropollutants in wastewater.

(Invited) Multi-Scale and Multi-Physics Modeling for Advancing Photoelectrochemical and Photocatalytic Material and Device Research

Modelling can efficiently support the choice of the most interesting conceptual design approaches, material choices, and operating conditions for photoelectrochemical and photocatalytic devices. Here, I will discuss modeling of three different ideas for versatile and cheap solar hydrogen and syngas production: i) photocatalytic particle suspended in a solution, ii) semiconductor particle-based photoelectrodes (PEs) fabricated by scalable dipping procedures, and iii) high-temperature approaches to photoelectrochemistry. Modeling of scalable photocatalysis suspensions require understanding of the single particle band energetics and kinetics and coupling it to the heat, mass and charge transport processes in a complete suspension. I will show how we use and couple 1D single particle models and 2D suspension simulations to provide material and design guidance of photocatalytic suspension approaches. Modeling of complicated particle-based PEs, on the other hand, requires full 3D multi-scale device models accounting for the morphological details of the nano-scale and then coupling them through homogenization theory to the macroscopic device model. I will show how we utilized nano-tomography to obtain the exact nano-scale morphology and how this morphology is incorporated into direct pore-level modeling to predict inhomogeneity in the variable fields and corresponding underutilization of parts of the PE. Finally, I will show how we use advanced 2D heat transfer models and detailed 1D junction models for mixed electron and ion conductor interfaces to model and explore high temperature approaches to photoelectrochemistry. I will end with a general outlook on modeling of photo-driven devices.

Life cycle assessment of novel consolidants and a photocatalytic suspension for the conservation of the immovable cultural heritage

Abstract Three innovative conservation materials were investigated by means of life cycle assessment (a calcium acetoacetate consolidant for carbonate surfaces, a TEOS-based consolidant for silicate substrates, and a photocatalytic suspension). So far not much attention has been paid to materials for the conservation of the built cultural heritage, with regard to their environmental performance. The main aim of this study was to assess the environmental footprint of the above-mentioned conservation materials which arises throughout their life cycle. In this way comparative data are made available for other future LCA studies on consolidants and photocatalytic suspensions. The most heavily polluting processes (i.e. “hotspots”) in the life cycle of the investigated conservation materials were identified, and, where possible, solutions for the further optimization of their environmental performance were proposed. In the case of life cycle of the two above-mentioned consolidants, the majority of emissions can be attributed to the synthesis of the constituent materials which are used to make the final products. Ethyl polysilicate is the largest contributor to the environmental footprint of the TEOS-based consolidant. On the other hand, in the life cycle of the calcium acetoacetate consolidant most of the environmental burdens are contributed by the synthesis of acetone-dicarboxylic acid. Around 0.47 kg of CO2 equivalent emissions affecting global warming are released to the air during the life cycle of 1 L of calcium acetoacetate (considering solely the upstream and core processes), whereas this value is higher in the case of the life cycle of the TEOS-based consolidant, i.e. 3.77 kg of CO2 equivalent emissions. In the case of the life cycle of the investigated photocatalytic suspension, although 1 L of this suspension is responsible for the release of only 0.1 kg of CO2 equivalent emissions over its life cycle (excluding the case-specific downstream processes) the heaviest environmental impact is caused by the production of packaging material (e.g. plastic buckets and other types of plastic containers). Taking into account the above-mentioned facts, there are not many possibilities for the reduction of the environmental burdens of the two investigated consolidants by the environmental optimization of the processes involved in the core and downstream stages of their life cycles. In the life cycle of the photocatalytic suspension, the environmental burdens related to greenhouse gas emissions could be reduced by more than 10% if a cleaner form of electricity production were to be adopted. A further aim of this paper is to promote sustainability in the field of management of the immovable cultural heritage. Although the described conservation materials have only a minor environmental effect in the field of the management of the immovable cultural heritage, the significance of sustainability is presented to conservators on a practical example.

Synergistic effect of the consolidant and the photocatalytic coating on antifungal activity of porous mineral substrates

Abstract The goal of the paper is the investigation of synergistic action of newly developed consolidants and LDH_TiO2 photocatalytic suspension on the characteristics (antifungal efficiency and surface properties) of the selected mineral substrates: brick and render. There were two different application protocols employed: protocol (1) the fresh photocatalytic suspension was applied on already consolidated substrates aged for 1, 2, 4 and 7 months, and protocol (2) only once on all specimens aged 1 month after the consolidant application. This study provides an insight into the synergistic effect of the applied materials on the antifungal activity, hydrophilicity and performances of the substrates’ surface during UV irradiation. The decrease of OH− ions on the surface, revealed from the photocatalytic suspension, showed a positive effect on the surface stability and antifungal properties of the mineral surface. Based on the obtained results, the most suitable protocol for the application of the photocatalytic suspension on the already consolidated and aged porous substrates has been adopted.

“One-Pot” Synthesis and Photocatalytic Hydrogen Generation with Nanocrystalline Ag(0)/CaTiO3 and in Situ Mechanistic Studies

We describe a previously not reported “one-pot” synthesis of nanocrystalline Ag(0)/CaTiO3 in aqueous suspension and the following in situ photocatalytic testing in the same suspension to generate hydrogen. The Ag(0)/CaTiO3 showed an enhancement of photocatalytic hydrogen generation rate vs CaTiO3 precursor. The obtained Ag(0)/CaTiO3 photocatalyst was ex situ characterized by XPS, XRD, UV–vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy, and concluded to have metallic silver nanoparticles on the surface of calcium titanate nanocrystals. The three photocatalytic mechanisms in Ag(0)/CaTiO3 were considered: (a) bandgap narrowing in CaTiO3, (b) enhanced electron–hole separation in CaTiO3, and (c) excitation of surface plasmon resonance (SPR) in metallic Ag nanoparticles. In mechanistic studies, photocatalytic suspensions with CaTiO3 precursor, with silver precursor, and with both CaTiO3 and Ag precursors to form Ag(0)/CaTiO3 were illuminated, flash-frozen to 77 K, and charact...

Establishing Efficient Cobalt-Based Catalytic Sites for Oxygen Evolution on a Ta3N5 Photocatalyst

In a photocatalytic suspension system with a powder semiconductor, the interface between the photocatalyst semiconductor and catalyst should be constructed to minimize resistance for charge transfer of excited carriers. This study demonstrates an in-depth understanding of pretreatment effects on the photocatalytic O2 evolution reaction (OER) activity of visible-light-responsive Ta3N5 decorated with CoOx nanoparticles. The CoOx/Ta3N5 sample was synthesized by impregnation followed by sequential heat treatments under NH3 flow and air flow at various temperatures. Various characterization techniques, including X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS), were used to clarify the state and role of cobalt. No improvement in photocatalytic activity for OER over the bare Ta3N5 was observed for the as-impregnated CoOx/Ta3N5, likely because of insufficient contact between CoOx and Ta3N5. When the sample was treated in NH3 at high temperature, a substantial improvement in the photocatalytic activity was observed. After NH3 treatment at 700 °C, the Co0–CoOx core–shell agglomerated cobalt structure was identified by XAS and STEM. No metallic cobalt species was evident after the photocatalytic OER, indicating that the metallic cobalt itself is not essential for the reaction. Accordingly, mild oxidation (200 °C) of the NH3-treated CoOx/Ta3N5 sample enhanced photocatalytic OER activity. Oxidation at higher temperatures drastically eliminated the photocatalytic activity, most likely because of unfavorable Ta3N5 oxidation. These results suggest that the intimate contact between cobalt species and Ta3N5 facilitated at high temperature is beneficial to enhancing hole transport and that the cobalt oxide provides electrocatalytic sites for OER.

A mathematical model to describe the photocatalytic reality: What is the probability that a photon does its job?

The purpose of this study is to present a simple methodology for predicting the performance of degradation of a photocatalytic system. The proposed model has the advantages of a minimal use of experimental data, and no introduction of adjustment variables. In our simulation we introduced a new parameter ψ reflecting the probability that a photon absorbed by the photocatalytic suspension gives an oxidizing agent. The first step in building our predictive model is to calculate, using Monte Carlo simulation, the absorbed energy per unit time and volume irradiated in space “LVRPA” for both types of selected photocatalysts (P25 and UV100). The second stage is to find an adequate theoretical kinetic model for the degradation of the primary pollutant (phenol) in different intermediates and ultimately to CO2 and H2O. The probability ψ serves to link the two previous steps in the selected mathematical environment. Our model is proven effective for predicting the kinetics of phenol degradation and its two intermediates: hydroquinone and benzoquinone. The global deviation between experimental data and model outputs were, for the primary pollutant, 12.18% for P25 and 9.63% for UV100, with ψP25=1.16% and ψUV100=0.88%.

Characterization of photocatalytically active coatings based on TiO2/Zn-Al layered double hydroxide on ceramic tiles

The self-cleaning function (photocatalytic activity and surface hydrophilicity/hydrophobicity) is of great importance for ceramic tiles from both economic and environmental point of view. This research is focused on the preparation of suitable photocatalytic suspensions studying the influence of the photocatalyst powder amount and the molecular mass of polyethylene glycol (PEG) on the self-cleaning properties of the suspensions deposited on the ceramic tile surface. Photocatalysts based on Zn-Al double layered hydroxides with TiO2 as active component, were synthesized and used for the preparation of the suspensions. The coated tiles prepared using smaller photocatalyst amount and the highest investigated molecular mass of PEG (PEG 4000) showed the highest photocatalytic activity in the Rhodamine B degradation reaction, as well as the appropriate surface properties.

Photocatalytic Suspension for Road Pavements: Investigation on Wearing and Contaminant Effects

AbstractPhotocatalytic technologies offer a unique benefit to road materials due to their potential to support depollution reactions of nitrogen oxide (NOx) and their versatility. The aims of this research were to investigate the wear resistance of photocatalytic asphalt slabs under repeated loads and to quantify the effect of contaminants such as dirt (fine particles), salt (sodium chloride) and deicing solution (salt plus water) on photocatalytic effectiveness. Accelerated loading tests (wheel tracking test) and skid resistance (British pendulum test) allowed the characterization of slab behavior over different steps of cycles. A specific laboratory setup was adopted to measure the reduction in concentration of pollutants as nitrogen oxide in accordance with European standards. Results showed a decrease over progressive load cycles in depolluting effectiveness and skid resistance of photocatalytic slabs, and deicing solution had the largest negative effect. The negative impact was largely dependent on t...

Ceramic tiles for photodegradation of Orange II solutions

The photocatalytic behaviour of several commercial titania powders (in aqueous suspension) was evaluated through the decolouration of Orange II aqueous solutions. The performance was correlated with relevant characteristics of the powders, such as crystalline phases, particle size and morphology.The highest efficiency TiO2 powders were those deposited by jet spray on ceramic tiles, and then fired to stabilise the layers. The obtained products were characterised and tested for the photocatalytic degradation of the Orange II dye, in a batch photoreactor under visible light irradiation. Values were compared with those achieved by TiO2 suspensions.The following experimental variables were tested: (i) the amount of deposited titania; (ii) powder manufacturer/source; (iii) firing temperature of deposited layers; and (iv) operation time.Optimal processed layers showed an interesting decolouration performance, as denoted by an attenuation degree of 96% and decolouration rate, assuming an apparent first order reaction, reaching 5.9×10−3min−1. Thus, these layered ceramic tiles can be considered as an alternative to photocatalytic suspensions of the oxide, with the advantage of avoiding the need to remove any photocatalyst particles at the end of the process. Besides the good photocatalytic performance, the optimized ceramic tiles have an aesthetically pleasing surface, a good adhesion to the substrate, and are easy to clean, thus fulfilling industrial/commercial requirements.

Photodegradation of Orange II solutions by TiO 2 active layers jet sprayed on aluminium sheets

In this work, active TiO 2 layers have been immobilized, on aluminium sheets, by a common and cheap deposition technique: jet spray. The layers’ adhesion to the substrate was achieved by mixing the titania with a commercial thermally adherent polyester ink, which is industrially used for aluminium surface treatment (lacquering). The layers’ photocatalytic performance was tested in the degradation of the organic dye Orange II in aqueous solutions, in a batch photoreactor under visible and solar light, and compared with TiO 2 (anatase) suspensions. The layers’ photocatalytic behaviour was evaluated taking into account different experimental variables, such as: (i) layer thickness; (ii) operation time; (iii) TiO 2/polyester ink weight ratio and (iii) dye solution concentration and pH. A better performance was attained for layers having a 1:1 weight ratio of TiO 2 and polyester ink and a thickness of 60 μm (100 g/m 2). These layers showed an interesting discolouration performance: an attenuation degree of 95% and discolouration rate, assuming an apparent first order reaction, reaching 2.2 × 10 −3 min −1. These results were attained for the naturally resulting dye solution pH of ≈7, and for the lowest dye concentration of 20 mg/L. Therefore, neither alkalinisation or acidification of the dye solution nor the utilization of high-concentration solutions is recommended. Despite the slower kinetics, the dye degradation level achieved is similar to that obtained for TiO 2 powder suspensions. Thus, these treated layered aluminium pieces can be considered as a serious alternative to photocatalytic suspensions of the oxide, with the advantage of excluding the removal of the photocatalyst at the end of the process.

Decolouration of Orange II solutions by TiO2 and ZnO active layers screen-printed on ceramic tiles under sunlight irradiation

Abstract In this work TiO 2 and ZnO layers have been deposited by screen-printing in common ceramic tiles. These layers were characterized and tested for the photocatalytic degradation of organic dye Orange II in aqueous solutions, under direct exposure to the sunlight. Optimal processed layers showed an interesting decolourisation performance, as denoted by an attenuation degree of 90% and decolouration rate, assuming an apparent first order reaction, reaching 2.9 × 10 −3 min −1 . In the actual conditions, TiO 2 layers show superior performance than ZnO. The previous alkalinisation of the dye solution is not recommended, since better performance is achieved under the naturally resulting pH (6.7) of the solution (20 g/L). Thus these layered ceramic tiles can be regarded as an alternative to photocatalytic suspensions of the same material with the advantage of avoiding the removal of the photocatalyst at the end of the process.