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A two-step process involving coagulation-flocculation followed by solar photocatalysis – based Advanced Oxidation Process (AOP) using TiO2-Reduced Graphene Oxide (TRGO) nanocomposite as catalyst ha...

Versatile sensing matrixes are essential for the development of enzyme-immobilized optical biosensors. A novel three-dimensional titanium dioxide nanotubes/alginate hydrogel scaffold is proposed for the detection of sweat biomarkers, lactate, and glucose in artificial sweat. Hydrothermally synthesized titanium dioxide nanotubes were introduced to the alginate polymeric matrix, followed by cross-linking nanocomposite with dicationic calcium ions to fabricate the scaffold platform. Rapid colorimetric detection (blue color optical signal) was carried out for both lactate and glucose biomarkers in artificial sweat at 4 and 6 min, respectively. The superhydrophilicity and the capillarity of the synthesized titanium dioxide nanotubes, when incorporated into the alginate matrix, facilitate the rapid transfer of the artificial sweat components throughout the sensor scaffold, decreasing the detection times. Moreover, the scaffold was integrated on a cellulose paper to demonstrate the adaptability of the material to other matrixes, obtaining fast and homogeneous colorimetric detection of lactate and glucose in the paper substrate when image analysis was performed. The properties of this new composite provide new avenues in the development of paper-based sensor devices. The biocompatibility, the efficient immobilization of biological enzymes/colorimetric assays, and the quick optical signal readout behavior of the titanium dioxide nanotubes/alginate hydrogel scaffolds provide a prospective opportunity for integration into wearable devices. The authors acknowledge support from Gobierno de Espana, Ministerio de Economia y Competitividad (Grant No. BIO2016-80417-P) (AEI/FEDER, UE), "Ministerio de Ciencia y Educacion de Espana" under grant PID2020-120313GB-I00/AIE/10.13039/501100011033 and the Basque Government (Grant IT1271-19). This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 766007. The authors convey their special thanks to SGIker of the University of the Basque Country (UPV/EHU) and Dr. Javier G. Inanez for the technical equipment facility support. F.B.-L. and L.B.-D. acknowledge the "Red de Microfluidica Espanola" RED2018102829-T.

Paper-TiO2-Ag2O floating photocatalysts were produced under mild condition and their photocatalytic activity for the degradation of aromatic amine under sunlight stimulant was investigated. Characterizations by Raman, XRD, XPS, DRS and PL confirmed the presence of TiO2 and Ag2O, and the morphology of the appended TiO2/Ag2O layer was probed by FE-SEM. The photocatalytic activity of the prepared samples was investigated by the degradation of aniline (AN) in water under simulated sun-light illumination and constrained conditions, i.e. non-stirring and non-oxygenation. The presence of Ag2O combined with TiO2 was shown to improve the resistance of paper to bacteria attack, thus increasing the durability of the photocatalyst. Thanks to its hydrophobic character, the paper-TiO2-Ag2O NPs can be employed as useful floating photocatalyst and can be reused in continuous cycles.

Two simple routes for the synthesis of a paper-TiO2 composite were tuned up and the efficiency of the resulting paper-TiO2 photocatalyst was investigated in the 2-propanol oxidation in gas phase. The first route involved the in-situ generation over the sheet of paper of a TiO2 layer starting from a solution of Ti (OBu)4 in tert-butanoliacetic acid, followed by hydrothermal treatment at 120 degrees C for 3 h. The sample was labelled as paper-TiO2 (H). The second approach was based on the adsorption on the paper of a ready-made suspension of titania nanoparticles (TiO2 sol), generated in autoclave at 140 degrees C and stable in acid medium at pH

In this work, an environmental friendly RC/N-TiO2 nanocomposite thin film was designed as a green portable photocatalyst by utilizing recycled newspaper as sustainable cellulose resource. Investigations on the influence of N-doped TiO2 nanorods incorporation on the structural and morphological properties of RC/N-TiO2 nanocomposite thin film are presented. The resulting nanocomposite thin film was characterized by FESEM, AFM, FTIR, UV-vis-NIR spectroscopy, and XPS analysis. The results suggested that there was a remarkable compatibility between cellulose and N-doped TiO2 nanorods anchored onto the surface of the RC/N-TiO2 nanocomposite thin film. Under UV and visible irradiation, the RC/N-TiO2 nanocomposite thin film showed remarkable photocatalytic activity for the degradation of methylene blue solution with degradation percentage of 96% and 78.8%, respectively. It is crucial to note that the resulting portable photocatalyst produced via an environmental and green technique in its fabrication process has good potential in the field of water and wastewater treatment application.

Producción Científica, Paper industry is adopting zero liquid effluent technologies to reduce fresh water use and meet environmental regulations, which implies water circuits closure and the progressive accumulation of pollutants that must be removed before water re-use and final wastewater discharge. The traditional water treatment technologies that are used in paper mills (such as dissolve air flotation or biological treatment) are not able to remove recalcitrant contaminants. Therefore, advanced water treatment technologies, such as advanced oxidation processes (AOPs), are being included in industrial wastewater treatment chains aiming to either improve water biodegradability or its final quality. A comprehensive review of the current state of the art regarding the use of AOPs for the treatment of the organic load of effluents from the paper industry is herein addressed considering mature and emerging treatments for a sustainable water use in this sector. Wastewater composition, which is highly dependent of the raw materials being used in the mills, the selected AOP itself, and its combination with other technologies, will determine the viability of the treatment. In general, all AOPs have been reported to achieve good organics removal efficiencies (COD removal >40%; and about an extra 20% if AOPs are combined with biological stages). Particularly, ozonation has been the most extensively reported and successfully implemented AOP at an industrial scale for effluent treatment or reuse within pulp and paper mills; although Fenton processes (photo-Fenton particularly) have actually addressed better oxidative results (COD removal ≈65-75%) at lab scale, but still need further development at large scale., Comunidad Autónoma de Madrid - (Proyecto P-2009/AMB/1480), Ministerio de Ciencia e Innovación - (Proyecto CIT-310000-2008-15)

The development of solid materials which are able to upconvert optical radiation into photons of higher energy is attractive for many applications such as photocatalytic cells and photovoltaic devices. However, to fully exploit triplet-triplet annihilation photon energy upconversion (TTA-UC), oxygen protection is imperative because molecular oxygen is an ultimate quencher of the photon upconversion process. So far, reported solid TTA-UC materials have focused mainly on elastomeric matrices with low barrier properties because the TTA-UC efficiency generally drops significantly in glassy and semicrystalline matrices. To overcome this limit, for example, combine effective and sustainable annihilation upconversion with exhaustive oxygen protection of dyes, we prepare a sustainable solid-state-like material based on nanocellulose. Inspired by the structural buildup of leaves in Nature, we compartmentalize the dyes in the liquid core of nanocellulose-based capsules which are then further embedded in a cellulose nanofibers (NFC) matrix. Using pristine cellulose nanofibers, a sustainable and environmentally friendly functional nanomaterial with ultrahigh barrier properties is achieved. Also, an ensemble of sensitizers and emitter compounds are encapsulated, which allow harvesting of the energy of the whole deep-red sunlight region. The films demonstrate excellent lifetime in synthetic air (20.5/79.5, O2/N2)-even after 1 h operation, the intensity of the TTA-UC signal decreased only 7.8% for the film with 8.8 μm thick NFC coating. The lifetime can be further modulated by the thickness of the protective NFC coating. For comparison, the lifetime of TTA-UC in liquids exposed to air is on the level of seconds to minutes due to fast oxygen quenching.

Phenol and its derivatives are the major environmental pollutants discharged from paper and pulp industries into water bodies. All these compounds and chlorinated phenolic compounds in particular are very toxic to fauna and flora, even at relatively low concentration. This study aimed to investigate the removal rate of phenolic compounds from the effluent of pulp and paper industries using a combination of ozonation and photocatalytic processes. Firstly, a certain volume from the effluent of paper and pulp industries containing certain phenol concentrations was obtained and fed into a prefabricated reactor at laboratory scale. Then, the combined and separate effects of zinc oxide dosage (ZnO), ozone flow rate (O3), and pH under ultra violet radiation for 30 min were evaluated. The concentration of phenolic compounds and the produced ozone gas flow rate were measured by a spectrophotometry and iodometric method, respectively. The results showed that the phenolic removal rate increased at acidic PHs compared with alkaline PHs; it was also decreased with the increase in ZnO dosages. Furthermore, the highest phenolic compound’s removal rate was 99% at the optimal condition (pH 5, ZnO dosage of 0.1 g L−1 at the 30 min with UV-C illumination of 125 W). Finally, Daphnia toxicity test showed that treated effluent was safe and met the standards to the extent that it can be discharged into the receiving waters.

Paper with antimicrobial properties was developed through in situ growth of ZnO nanorods. The targeted application for this type of paper is in health centers as wallpaper, writing paper, facemasks, tissue paper, etc. The paper was tested on three model microbes, Gram-positive bacteria Staphylococcus aureus, Gram-negative bacteria Escherichia coli and common airborne fungus Aspergillus niger. No viable bacterial colonies or fungal spores could be detected in the areas surrounding test samples of the antimicrobial paper. Gram-negative bacteria Escherichia coli were found to be inhibited in an area that is 239% and 163% the area of the paper sample under different room lighting conditions, i.e., halogen and fluorescent lamp illumination, respectively. For Gram-positive bacteria Staphylococcus aureus the zones of inhibition surrounding the paper samples are 102% and 70%, and for Aspergillus niger, 224% and 183% of the sample area, under similar lighting conditions.

Nanomaterials with unique electronic, optical and catalytic properties have recently been at the forefront of research due to their tremendous range of applications. Taking gold, silver and titania nanoparticles as examples, we have reviewed the current research works on paper functionalized by these nanoparticles. The functionalization of paper with only a very small concentration of nanoparticles is able to produce devices with excellent photocatalytic, antibacterial, anti-counterfeiting, Surface Enhanced Raman Scattering (SERS) and Surface Plasmon Resonance (SPR) performances. This review presents a brief overview of the properties of gold, silver and titania nanoparticles which contribute to the major applications of nanoparticles-functionalized paper. Different preparation methods of the nanoparticles-functionalized paper are reviewed, focusing on their ability to control the morphology and structure of paper as well as the spatial location and adsorption state of nanoparticles which are critical in achieving their optimum applications. In addition, main applications of the nanoparticles-functionalized papers are highlighted and their critical challenges are discussed, followed by perspectives on the future direction in this research field. Whilst a few studies to date have characterized the distribution of nanoparticles on paper substrates, none have yet optimized paper as a nanoparticles' substrate. There remains a strong need to improve understanding on the optimum adsorption state of nanoparticles on paper and the heterogeneity effects of paper on the properties of these nanoparticles.

Reactive black 5 (RB5), an azo dye, was degraded by using UV-irradiated TiO 2 coated on non woven paper with SiO 2 as a binder. The adsorption capacity of the photocatalyst was studied at natural pH, superior to pH pzc of the binder, for various ionic strengths. Different salts such as NaCl, KCl, CaCl 2 , LiCl, Ca(NO 3 ) 2 were used to increase the ionic strength. The presence of salt increased the adsorption capacity. The electrostatic interactions between dye and oxide surface charges (TiO 2 /SiO 2 ) is very important in the adsorption phenomena. The effect of the ionic strength of the solution on photocatalyst degradation was studied. The rate of degradation was increased by the presence of salts in the range of the experimental conditions. The increase of the initial decolorization rate was observed in the following order: Ca 2+ > K + > Na + > Li + . Experiments with different anions (Cl − , NO 3 − ) had shown that nitrate was an indifferent electrolyte for the adsorption and photodegradation of the dye on SiO 2 /TiO 2 .

Photocatalytic paper sheets were prepared by addition of different ratios of TiO2/Sodium alginate (TSA) nanocomposite. The modified paper sheets were characterized by XRD, TGA. Their morphology was studied by scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Photocatalytic activity of modified paper has been studied by analysis of chemical oxygen demand (COD) of waste-water. The results confirmed the mineralization of the waste-water and enhanced removal of chemical oxygen demand (COD) by increasing the amount of photocatalyst in the paper. Moreover, the results also confirmed that presence of sodium alginate as biopolymer increased adhesion of nanoparticles to paper fibers and reduced the harmful effect of the photocatalyst on them. The paper sheets containing 7% as well as 15% TSA showed high photocatalytic activity and anti-bacterial effect against Salmonella typhimurium higher than standard antibiotic beside other microorganisms such as Candida albicans. The maximum antimicrobial effect was found in case of specimen loaded with 15% TSA. Moreover, it was found that by adding 20% TSA to the paper matrix, the properties of the paper composite collapse. The obtained results confirm the possible utilization of the modified paper in both hygienic and food packaging applications.

Photocatalytic paper encompasses a range of materials based on paper and nonwoven fabrics which performs a function based on the light-activated catalytic activity of colloidal TiO(2). The literature describing photocatalytic paper is surveyed, including mechanisms, applications, limitations and future opportunities. The technology is in its infancy with less than 10 patents and as many scientific publications appearing over the last decade. The main applications described are the destruction of organic molecules (mineralization) and photo-disinfection (sterilization). These disclosures build upon a much larger literature describing photochemical properties of TiO(2) both supported on non-cellulose substrates or simply as suspended particles in water or air. Current photocatalytic paper developments include methods to fix TiO(2) to cellulose substrates to minimize photochemical damage to the paper. Another theme is the use of multiple approaches, such as zeolites, for enhanced mineralization, and metals, such as silver and copper, for enhanced photocatalytic disinfection.

Different advanced oxidation processes (AOPs) have been applied to remove the organic carbon content of a paper mill effluent originating from the Kraft pulp bleaching process. The considered AOPs were: TiO2-mediated heterogeneous photocatalysis, TiO2-mediated heterogeneous photocatalysis assisted with H2O2, TiO2-mediated heterogeneous photocatalysis coupled with Fenton, photo-Fenton, ozonation and ozonation with UV-A light irradiation. The application of the selected AOPs all resulted in a considerable decrease in dissolved organic carbon (DOC) content with variable treatment efficiencies depending upon the nature/type of the applied AOP. A Life Cycle Assessment (LCA) study was used as a tool to compare the different AOPs in terms of their environmental impact. Heterogeneous photocatalysis coupled with the Fenton’s reagent proved to have the lowest environmental impact accompanied with a moderate-to-high DOC removal rate. On the other hand, heterogeneous photocatalysis appeared to be the worst AOP both in terms of DOC abatement rate and environmental impact. For the studied AOPs, LCA has indicated that the environmental impact was attributable to the high electrical energy (power) consumption necessary to run a UV-A lamp or to produce ozone.

A novel paper-based material containing titanium dioxide (TiO(2)) photocatalyst was successfully prepared by a papermaking technique with the internal addition of inorganic fibers on which TiO(2) particles were supported. Photodegradation performance of acetaldehyde gas, an indoor pollutant, and the durability of the TiO(2)-containing papers were investigated under UV irradiation. Ceramic fiber suspension and polydiallyldimethylammonium chloride as a cationic flocculant were mixed, followed by the addition of TiO(2) suspension and anionic polyacrylamide. Subsequently, the inorganic mixture was poured into a pulp suspension, and TiO(2) handsheets then prepared by a papermaking method. The tensile strength of TiO(2)-containing paper without a ceramic carrier decreased by more than 30% after 240-h UV irradiation (2 mW/cm(2)), although the strength of the TiO(2) sheet with ceramic fibers remained reasonably stable. The efficiency of acetaldehyde decomposition by the TiO(2) paper containing an inorganic carrier was nearly equal to that of the carrier-free TiO(2) paper. Scanning electron microscopic observation suggested that most TiO(2) particles were predominantly supported on the inorganic fiber matrix, and were mostly out of contact with organic pulp fibers. The TiO(2) paper with an inorganic carrier demonstrated both excellent photocatalytic performance and durability, which before had been mutually incompatible for organic materials containing TiO(2) photocatalyst. The two-stage mixing procedure for TiO(2) sheet-making is promising for the simple manufacture of high performance paper with photocatalytic ability.

Titanium dioxide (TiO2) photocatalyst and zeolite adsorbent were made into a paper-like composite by a papermaking technique using pulp and ceramic fibers as sheet matrix. The photocatalytic performance for the degradation of bisphenol A (BPA) dissolved in water was investigated under UV irradiation. The TiO2 sheet prepared was easier to handle than the original TiO2 powders in aqueous media. The TiO2 sheet could decompose the BPA under UV irradiation, although at a lower degradation efficiency than the TiO2 suspension. The TiO2-free zeolite sheet could not remove the BPA from water completely because of its adsorption equilibrium. Furthermore, the composite TiO2-zeolite sheets exhibited a higher efficiency for BPA removal than the zeolite-free TiO2 sheets, the efficiency of the former being equivalent to that of the TiO2 suspension. The enhancement in removal efficiency was not attributed to the simple adsorption of BPA on zeolite but rather to the synergistic effect obtained through the combined use of TiO2 photocatalyst and zeolite adsorbent in the paper-like composite sheet, which is believed to accelerate the BPA photodegradation in water.

Paper-based devices provide an alternative technology for simple, low-cost, portable, and disposable diagnostic tools for many applications, including clinical diagnosis, food quality control, and environmental monitoring. In this study we report a two-step fabrication process for creating two-dimensional microfluidic channels to move liquids on a hydrophobized paper surface. A highly hydrophobic surface was created on paper by TiO2 nanoparticle coating using a high-speed, roll-to-roll liquid flame spray technique. The hydrophilic pattern was then generated by UV irradiation through a photomask utilizing the photocatalytic property of TiO2. The flow dynamics of five model liquids with differing surface tensions 48-72 mN·m(-1) and viscosities 1-15 mN·m(-2) was studied. The results show that the liquid front (l) in a channel advances in time (t) according to the power law l=Zt0.5 (Z is an empirical constant which depend on the liquid properties and channel dimensions). The flow dynamics of the liquids with low viscosity show a dependence on the channel width and the droplet volume, while the flow of liquids with high viscosity is mainly controlled by the viscous forces.

According to current environmental legislation concerned with water scarcity, paper industry is being forced to adopt a zero liquid effluent policy. In consequence, reverse osmosis (RO) systems are being assessed as the final step of effluent treatment trains aiming to recover final wastewater and reuse it as process water. One of the most important drawbacks of these treatments is the production of a retentated stream, which is usually highly loaded with biorecalcitrant organic matter and inorganics; and this effluent must meet current legislation stringent constraints before being ultimately disposed. The treatment of biorefractory RO retentate from a paper mill by several promising advanced oxidation processes (AOPs) – conventional Fenton, photo-Fenton and photocatalysis – was optimized considering the effect and interaction of reaction parameters; particularly using response surface methodology (RSM) when appropriate (Fenton processes). The economical cost of these treatments was also comparatively assessed. Photo-Fenton process was able to totally remove the COD of the retentate, and resulted even operatively cheaper at high COD removal levels than conventional Fenton, which achieved an 80% reduction of the COD at best. In addition, although these optimal results were produced at pH = 2.8, it was also tested that Fenton processes are able to achieve good COD reduction efficiencies (>60%) without adjusting the initial pH value, provided the natural pH of this wastewater was close to neutral. Finally, although TiO2-photocatalysis showed the least efficient and most expensive figures, it improved the biodegradability of the retentate, so its combination with a final biological step almost achieved the total removal of the COD.

Cellulose and paper pulp factories utilize a large amount of water generating several undesirable contaminants. The present work is a preliminary investigation that associates the electrocoagulation–flotation (EC) method followed by photocatalysis to treat such wastewater. For EC, the experiment with aluminium and iron electrodes showed similar efficiency. Iron electrodes (anode and cathode) were chosen. By applying 30 min of EC/Fe 0 , 153 A m −2 and pH 6.0, the COD values, UV–vis absorbance and turbidity underwent an intense decrease. For the subsequent UV photocatalysis (mercury lamps) TiO 2 was employed and the favourable operational conditions found were 0.25 g L −1 of the catalyst and solution pH 3.0. The addition of hydrogen peroxide (50 mmol L −1 ) highly increased the photo-process performance. By employing the UV/TiO 2 /H 2 O 2 system, the COD reduction was 88% compared to pre-treated effluents and complete sample photobleaching was verified. The salt concentration on EC (iron electrodes) showed that the electrolysis duration can be reduced from 30 to 10 min by the addition of 5.0 g L −1 of NaCl. The biodegradability index (BOD/COD) increased from 0.15 (pre-treated) to 0.48 (after EC) and to 0.89 (after EC/photocatalysis irradiated for 6 h), showing that the employed sequence is very helpful to improve the water quality. This result was confirmed by biotoxicity tests performed with microcrustaceous Artemia salina .

In this study a poorly biodegradable (BOD/COD = 0.3) industrial alkaline ECF bleaching filtrate was treated using different advanced oxidation processes to evaluate their use in combined chemical–biological treatment aimed at increasing recalcitrant COD removal and improving final effluent quality. Oxidative treatments included ozonation combined with hydrogen peroxide (2, 5, 10, 20 mmol L −1 O 3 /0.7, 2, 5, 10 mmol L −1 H 2 O 2 ) and photocatalysis with hydrogen peroxide (UV/2, 4 and 8 mmol L −1 H 2 O 2 ) and with TiO 2 (UV/TiO 2 /0.7 and 4 mmol L −1 H 2 O 2 ). The O 3 /H 2 O 2 process increased effluent biodegradability by up to 68% as a result of increasing BOD and decreasing COD. Increasing the O 3 dose had a greater effect on biodegradability improvement and lignin and colour removal efficiencies than increasing the H 2 O 2 dose. A combined oxidant dose of 5 mmol L −1 O 3 and 2 mmol L −1 H 2 O 2 resulted in 75% lignin removal, 40% colour removal and 6% carbohydrate loss without mineralizing the organic carbon. The photocatalytic processes led to a decrease in effluent biodegradability through combined decrease in BOD and increase in COD and did not result in efficient lignin or colour removal. Photocatalytic oxidation was apparently inhibited by the high chloride and COD levels in the alkaline filtrate, and may be more efficient in recalcitrant COD removal if performed after biological.

The photocatalytic degradation of lignin obtained from wheat straw kraft digestion has been investigated by using TiO 2 and ZnO semiconductors. ZnO has been found to be a better photocatalyst than TiO 2 . The different variables studied, include catalyst dose, solution pH, oxidant concentration and initial concentration of the substrate. The degradation of lignin was favorable at pH 11. Optimum values of catalyst dose and oxidant concentration were found to be 1 g/l and 12.2 × 10 −6 M, respectively. The degradation of the organic compound was also evaluated as COD removal and increase in the COD removal was observed with increase in degradation rate. An attempt has also been made to explore the applicability of ZnO in immobilized mode for the degradation of lignin under solar light for industrial scale application. Further the comparative evaluation of ZnO in slurry/immobilized mode has been carried out.

TiO2 powder-containing paper composites, called TiO2 paper, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO2 paper has a porous structure originating from the layered pulp fiber network, with TiO2 powders scattered on the fiber matrix. Under UV irradiation, the TiO2 paper decomposed gaseous acetaldehyde more effectively than powdery TiO2 and a pulp/TiO2 mixture not in paper form. Scanning electron microscopy and mercury intrusion analysis revealed that the TiO2 paper had characteristic unique voids ca. 10 μm in diameter, which might have contributed to the improved photocatalytic performance. TiO2 paper composites having different void structures were prepared by using beaten pulp fibers with different degrees of freeness and/or ceramic fibers. The photodecomposition efficiency was affected by the void structure of the photocatalyst paper, and the initial degradation rate of acetaldehyde increased with an increase in the total pore volume of TiO2 paper. The paper voids presumably provided suitable conditions for TiO2 catalysis, resulting in higher photocatalytic performance by TiO2 paper than by TiO2 powder and a pulp/TiO2 mixture not in paper form.

Toluene and formaldehyde are malodorous and cause indoor pollution. These materials have received much attention as hazardous and malodorous substances. It is well known that long-term exposure to even fairly low levels of toluene and formaldehyde brings about the risk of asthma and eczema. In this study, a composite TiO2–zeolite (ZE) sheet prepared using a papermaking technique was applied to remove toluene and formaldehyde under UV irradiation. The optimum composition of the TiO2 (Ti)–ZE sheet was studied in detail with regard to the effective removal of various indoor pollutants. Gaseous toluene and formaldehyde were removed by a composite TiO2–ZE sheet with different efficiencies depending upon the ratio of Ti/ZE in the composite sheet. The composite sheets could decompose formaldehyde and toluene repeatedly after being recharged. It was shown that the sheets are potentially applicable as highly functional materials to be placed on walls and ceilings of houses for the removal of various indoor pollutants.

Photocatalysis using ZnO-Fe2O3 coupled catalyst removed partially the organic matter dissolved in kraft black liquor obtained from pinus wood cooking. The photo-assisted oxidation using different ZnO/Fe2O3 ratios was studied following the CO, evolution during the course of the reaction. A synergy of the composite improves the mineralization observed. The optimal ZnO to Fe2O3 ratio varied from 0.5 to 0.7 which allowed the highest mineralization rates.

In this paper, the performance of a photoassisted electrolysis process, for the degradation of organic pollutants, is investigated. Results obtained in this work have shown that the thermally prepared anode of titanium, coated with 70TiO2/30RuO2, exhibits photoactivity and may be used for the treatment of effluents. A synthetic phenol aqueous solution and a real paper mill industry effluent were treated. Kinetic analysis showed a synergetic effect of electrolysis and photocatalysis and degradation rates are an order of magnitude greater than the sum of the results reached by using both processes individually. Using a 125 W mercury bulb and 20 mA cm-2, the phenol concentration decayed 85% in 90 min and 70% reduction of TOC was obtained. In the application of the treatment process for the degradation of the E1 bleach Kraft mill effluent, total phenols were practically eliminated in a short period of processing time, and color, usually resistant to biological treatment, was reduced to 10% from its initial value measured in terms of absorbance. Reductions of AOX, COD, and BOD by 25%, 30%, and 35%, respectively, were also observed.

A cellulose bleaching effluent (E1) was degraded in batch conditions by photocatalysis using TiO2 and ZnO supported on glass Raschig rings. The effluent was completely decolourised and the total phenol content was reduced by 85% after 120 min treatment with both catalysts. Partial mineralization of the organic matter was confirmed by total organic carbon (TOC) reduction, approximately 50%. The residual organic matter shows a low acute toxicity as compared to the initial values and AOX values are strongly reduced after the photocatalytic oxidation. Molecular mass distribution showed that high molecular mass compounds were almost completely degraded.

The oxidation of a 186 ppm 6-chlorovanillin solution was performed using impregnated TiO2 glass rings in a 1 l photochemical reactor. Fifty per cent degradation was obtained after 60 min with recirculation of the solution. Then, oxidised samples were submitted under aerobic conditions to bacterial degradation in the Pseudomonas paucimobilis (S37) and Burkholderia cepacia (PZK). Both selected aerobic bacteria degrade more efficiently the photocatalysed samples, being PZK strain better than S37. A first-order kinetic was observed in both systems photocatalytic and bacterial degradation.

The degradation, by several advanced oxidation reactions, of a pulp mill ECF bleaching effluent, was studied. The initial biodegradability of the organic matter present in the effluent, estimated as the BOD5/COD, was low (0.3). When the effluent was submitted to ozonation and to five different advanced oxidation systems (O3/UV, O3/UV/ZnO, O3/UV/TiO2, O2/UV/ZnO, O2/UV/TiO2), the biodegradability increase significantly. After five minutes of reaction, the O3/UV system appears as the most efficient in to transform the organic matter to more biodegradable forms. A similar effect was observed when the effluent was submitted to an activated sludge treatment. The COD, TOC and toxicity reduction correlated well with the biodegradability enhancement after AOPs treatments.