TiO2 Suspensions Research Articles

Titanium-based photocatalytic coatings for bacterial disinfection: The shift from suspended powders to catalytic interfaces

Accessibility to a clean indoor environment is still an important problem in the world. Photocatalysis based on semiconductor materials was proposed as a green solution for contaminated surfaces and domestic areas. This treatment has been considered by many researchers using diverse preparation methods. Titanium dioxide (TiO2) was extensively investigated to treat dyes and microorganisms in wastewater, indoor air and even in wild environments. TiO2 showed divergent efficacy against Gram+ and Gram- bacteria, viruses (DNA-viruses, RNA-viruses, and/or reverse transcribing viruses), algae (unicellular, microalgae…) and free-floating genomic DNA. Today, photocatalysis mediating TiO2 for pollutants removal in real settings is attracting a lot of attention. TiO2 absorbs in the UV spectral region and many techniques were adopted to red shift its absorption to the visible region such as doping, coupling with other semi-conductors or decorating it with plasmonic materials. TiO2 uses started as suspended material in aqueous media. This suspension was fast faced by the difficulty to recover the catalyst after treating water. In the present review, we present the shift from the photocatalytic activity of Ti-based catalysts/photocatalysts for the disinfection of polluted water (TiO2 in suspension) to the implementation of smart indoor surfaces (supported TiO2) presenting self-sterilizing properties. In this review, we present the general context of the water issue as raised by the United Nations 2030-agenda, we show an overview of photocatalytic materials and we try to link the reported photocatalytic mechanisms for the disinfection process. At the end of this review, we stress the advantages of using supported photocatalytic thin films and the interfacial phenomena leading to bacterial killing without sacrificing the catalyst that can be easily reused.

Glycerol as an excellent hydrogen and electron source for photocatalytic hydrogenation of nitrobenzene in water

The development of a new method for effective utilization of glycerol dissolved in water is needed. In this study, glycerol was used not as an energy source and a starting compound but as an electron and hydrogen source for photocatalytic hydrogenation of nitrobenzene in an aqueous suspension of TiO2 under various conditions. The function of glycerol as an electron and hydrogen source was compared with that of other C3-alcohols and glycols. The results showed that glycerol works most efficiently as an electron and hydrogen source and that electrons extracted from glycerol are directly used for the hydrogenation without formation of other products such as H2. The photocatalytic hydrogenation was also examined under solar light with and without stirring. Important factors for the electron and hydrogen source in the photocatalytic reaction in an aqueous medium are discussed on the basis of the results.

Study of process parameters of the atomizer-based spray gun for the application of a temporary matte coating for 3D scanning purposes

The aim of this paper is to find the most suitable process parameters of the spray gun for the deposition of matte coating for 3D optical scanning purposes. The membrane atomizer-based spray gun is used as a coating device. A suspension of TiO2 and ethanol is used as a coating material. In this study, the formed spray is analyzed using Phase Doppler Anemometry and the results are compared to the deposited coatings. Applied coatings are further examined using a profilometer and 3D scanner to analyze their thickness and the effect they have on the 3D surface reconstruction. The results of this work show that two spray layers are sufficient to evenly apply a coating with good properties for 3D optical scanning purposes. The coating thickness is below 1 μm, reference area is entirely scanned, and the scanned point cloud has a standard deviation from the reference plane below 1.1 μm.

Thermal crosslinking synthesis of ethylene-vinyl acetate copolymer supported floating TiO2 photocatalyst: characterization and photocatalytic performance.

Floating photocatalyst is of extensive interest due to easy recovery and efficient light harvest. Support materials largely determine the stability of floating photocatalysts and their synthesis complexity. Thus, finding proper floating supports is very important. Herein, ethylene-vinyl acetate copolymer (EVA) was investigated as a support to prepare floating TiO2/EVA using a simple thermal crosslinking procedure. Multiple characterization analyses demonstrated that TiO2 was anchored onto EVA surface evenly via hydrogen-bond-enhanced physical crosslinking and remained its virgin crystal structure. Photocatalytic experiments showed that the removal efficiency of Rhodamine B (RhB) by floating TiO2/EVA increased by 33.8% as compared to suspended particle TiO2. The h+ and ·O2- played dominant roles in TiO2/EVA-driven RhB degradation. A 30-day stability test demonstrated that TiO2/EVA had a high thermal, pH, and photo- stability. The three-run reuse test proved that TiO2/EVA exhibited satisfactory reusability. This study provides a new option for floating photocatalyst synthesis.

Synthesis, characterization, and photocatalytic performance of methyl orange in aqueous TiO2 suspension under UV and solar light irradiation

Nano-crystalline titanium dioxide (TiO2) photocatalyst has been extensively utilized in the last few decades because of its strong oxidizing power, redox selectivity, and higher photocatalytic performance. In this work, TiO2 nanoparticle (NPs) was synthesized, characterized, and applied for the degradation of methyl orange (MO) dye in an aqueous solution under UV and solar light irradiations. The XRD results showed dominated anatase phase (82%) with a smaller crystalline size (18.23 nm). A rough surface with a uniform spherical shape was observed by SEM analysis. FTIR and UV–Vis/DRS spectroscopy confirmed the stretching vibration of the hydroxyl groups and higher absorption edge towards longer wavelength with smaller bandgap energy (3.12 eV) of TiO2 lattice structure. The activity of TiO2 NPs was carried out from the degradation of MO dye as a model contaminant for textile effluent in presence of UV/solar irradiation. The photodegradation efficiency of MO dye (15 mg L−1) was observed at 85.90% and 96.38% for 0.150 g and 0.030 g of TiO2 NPs at natural pH (7.0), after 5 h of UV and solar light irradiation. The respective rate constants were determined to be 0.0063 min−1 and 0.01 min−1 for UV and simulated solar light irradiation respectively, and exhibited the best-fitted kinetic model of pseudo-first-order. The photodegradation efficiency was increased with the decrease of pH, while efficiency decreased with an increase in initial dye concentration. The obtained result from TiO2 NPs was compared with commercially available Degussa P25 catalyst. The photocatalyst reusability test and reaction mechanism were also evaluated. The study suggests that TiO2 NPs are a promising photocatalyst that can be used for the degradation of organic dye compounds from textile wastewater towards the sustainable management of environment.

UVA LEDs and solar light photocatalytic oxidation/ozonation as a tertiary treatment using supported TiO2: With an eye on the photochemical properties of the secondary effluent

Photocatalytic oxidation/ozonation of a mixture of eight pharmaceuticals added to a secondary effluent, SE, of an urban wastewater treatment plant has been studied using TiO2 supported on commercial Al2O3/SiO2 ceramic foams. As radiation source UVA LEDs (365 nm) or solar radiation was used. Pharmaceuticals were added at high (1 mg L−1 each) or relatively low (50 μg L−1 each) concentration, contributing 25% and 1.5% to the initial TOC, respectively. Under both types of radiation, the photolysis of SE generated reactive species capable of degrading the contaminants (indirect photolysis), this effect being greater at lower initial concentration of pollutants. Lower concentration of contaminants also favoured their degradation and the SE mineralization by photocatalytic oxidation, whereas its effect on ozonation was low. The best results were obtained by photocatalytic ozonation, especially in terms of COD removal, without observing any synergism or antagonism between O3/Radiation and TiO2/Radiation systems. In SE, the performance of the supported catalyst resulted much better than that of suspended TiO2 P25, which showed almost no activity in this matrix. Through different cycles of reuse, the stability of the supported catalyst was confirmed.

RETRACTED: Evaluation of heat and mass transfer characteristics in a nanofluid flow over an exponentially stretchable sheet with activation energy

The current study explores the impact of heat source/sink on the flow of nanofluid across an exponentially stretchable sheet with the suspension of TiO2 as nanoparticle in base liquid water. Furthermore, activation energy, Newtonian heating and porous medium are accounted in the modelling. The modelling equations are transformed into a system of ordinary differential equations (ODEs) using similarity transformations. To solve these equations numerically, the Runge Kutta Fehlberg 45 (RKF 45) method and shooting approach are used. Graphical representations are used to study and address the effect of important factors on flow fields, heat, and mass transfer rates. The outcome reveals that, rising values of porous and suction parameters declines the velocity field. The rise in values of heat source/sink parameter declines the heat transfer. Moreover, rate of declination in heat transfer is faster for Newtonian heating (NH) case than common wall temperature (CWT) case. The rise in values of volume fraction and heat source/sink parameter declines the Nusselt number for both CWT and NH cases. Further, the fluid shows improved rate of heat transfer for CWT case than NH case.

Hydrophilic and hydrophobic TiO2 coatings by pulsed electrophoretic deposition

Hydrophobic and hydrophilic coatings have been widely studied because of their functions such as anticorrosion and self-cleaning. In this study two different TiO2 suspensions, obtained by dispersing of hydrophilic and hydrophobic TiO2 particles in ethanol, were used for preparation of titania coatings on stainless steel substrates by pulsed electrophoretic deposition (EPD). The resultant hydrophilic and hydrophobic rytile TiO2 coatings showed random orientation and are dense with no cracks. The thicknesses of the coatings obtained using hydrophilic and hydrophobic TiO2 particles were 22.5 and 20.1 ?m, respectively, whereas thier contact angles were 6.3? and 124.0?, respectively. The results show that hydrophilic and hydrophobic TiO2 coatings can be performed using pulsed EPD.

Comparison of reflectance to solar radiation between mortars treated with TiO2 and painted mortars after three years of exposure

The incident solar radiation on the building envelope is strongly affected by the urban characteristics and building facade materials. This paper reports a study on the variation in the solar reflectance of mortar specimens with different treatments of TiO2 – powder (addition) and suspension (cover) - compared with white painted specimens and exposed in the long term. The solar reflectance of mortars was evaluated at biweekly intervals over three years to reach their degradation over time. The results obtained for the white painted specimens revealed that they practically maintained the exact value of their initial reflectance to solar radiation over three years of exposure ending with 73% of its index. In addition, the comparison between the white painted specimens and specimens with TiO2 powder addition showed a mean solar reflectance difference of 28.25%, showing that difference certainly would be noticed by the final user in terms of absorption and color change. The study also revealed that comparison between the specimens with TiO2 in powder addition and specimens with TiO2 in suspension showed a mean solar reflectance difference of 8.5% and demonstrate that result will not identify by the final user concerning the absorption and color change, and not indicate their preference since both showed the same effectiveness in mean after three years of exposure.

Enhanced degradation of 2,6-dimethylphenol by photocatalytic systems using TiO2 assisted with H2O2 and Fe(III)

ABSTRACT In this study, several photocatalytic degradation systems were investigated using 2,6-dimethylphenol (2,6-DMP) as a model compound. Highly reactive species are formed in four systems, Fe(III), TiO2, TiO2/H2O2 and TiO2/Fe(III) where complete degradation of 2,6-DMP was achieved under UV radiation. Photodegradation of the 2,6-DMP has been described by pseudo-first order kinetic model in the presence of TiO2. In UV/TiO2–H2O2 system, the addition of H2O2 in the TiO2 suspension improves the degradation rate of 2,6-DMP from 70% to 100% for a H2O2 concentration of 10− 2 M in 3 h. In homogeneous system, HO• and Fe2+ can be generated by the irradiation of Fe(III) solution. The speciation of Fe(III) obtained from Visual MINTEQ soft showed the formation of several species and Fe(OH)2+ were the most predominant and active species in a pH range of 2.5–3.5. At a low concentration of TiO2 (30 mg L−1), an important positive effect due to the iron addition has been shown in TiO2/Fe(III) system, the entrance of metallic ions at different concentrations enhanced the photocatalytic activity of TiO2. A degradation percentage of 90% was achieved in the UV/TiO2–Fe(III) system under optimal conditions against 57% in UV/TiO2 system. Strong synergistic effect was observed in the UV/TiO2–H2O2 binary system. On the basis of literature, a pathway for 2,6-DMP degradation was proposed. The mechanism of degradation of the 2,6-DMP did not involve only HO• radicals, an interaction of Fe(III) in the excited state with 2,6-DMP occurred giving rise to the formation of 2,6-dimethylphenoxyl radical.

UV photoelectrocatalytic degradation of m- cresol pollutant using TiO2 dip -coated stainless steel electrode system

In the present study, the removal of m- cresol in an aqueous medium was studied by the photoelectrocatalytic (PEC) degradation by the TiO2 suspension on dip-coated stainless steel electrode under UV lamp of the wavelength of 352nm. The performance of the PEC method on the degradation of m- cresol was studied by made the comparison with the photocatalytic oxidation (PCO) method in terms of COD removal and kinetic study. In the PEC study on the degradation of m- cresol pollutant was studied by the various parameters such as initial concentration, pH, and the bias potential. The result found that the optimum degradation efficiency of m- cresol in the PEC and PCO methods were 79.6% and 39.8% at pH 5.0. The result showed that the kinetic constants (k) in the PEC and PCO methods were -0.0116 and -0.0058 under optimum conditions. The result found that the PEC method using TiO2 coated on stainless steel electrode is two times higher than the PCO method on the degradation of m- cresol.

Enhanced Electrical Properties of Crystalline Silicon Solar Cells via Nano-Composite Polyvinyl-Alcohol/Titanium Dioxide

Reflection loss and solar cell temperature both have a significant impact on solar cell efficiency and, consequently, on power generation. Herein, the aim is to investigate into the impact of Nanocomposite Titanium Dioxide (TiO2)/Polyvinyl Alcohol (PVA) on polycrystalline silicon solar cells. The solvent casting method is employed to prepare nanocomposite TiO2/PVA for deposition on the front side of the solar cell. The Tauc plot is used to investigate the influence of TiO2 nanoparticle concentration (10-20nm) on the energy bandgap of a nanocomposite. To test the optical properties of the solar cell after depositing the Nanocomposite coating film and to confirm the suspension of TiO2 in PVA and construct a Nanocomposite, an ultraviolet-visible spectrometer and a Fourier transform infrared spectrometer are provided. The results show that increasing the TiO2 in the TiO2/PVA Nanocomposite increases the energy bandgap. The Ultraviolet-Visible spectrometer observes that the Nanocomposite films absorb the Ultraviolet wavelength and transmittance at the visible wavelength. Finally, it found the lowest reflection obtained was 3.9% for 0.2wt% TiO2 in TiO2/PVA nanocomposite and the enhancement of the solar cell efficiency was (+2.3%).

Titania-silica Composite with Photocatalytic Properties and Its Application on Brazilian Granite and Sandstone

ABSTRACT The aim of the study described in this article was to evaluate a product containing titania (titanium dioxide, TiO2) applied on stones — particularly two types used at Brazilian stone-built heritage sites — that have been exposed to weathering and anthropogenic activities. This product was prepared by producing a suspension of TiO2 at two concentrations (1% and 4% w/v) with tetraethyl orthosilicate (TEOS) in the presence of n-octylamine as surfactant. The characteristics of the TiO2 were then observed by scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface-area measurements, particle-size distribution analysis (CILAS) and X-ray diffraction. After applying the TiO2-TEOS composite, the stones were examined for contact angle, spectrophotometry, sorptivity, thermal shock resistance, and UV-radiation resistance. The product proved ineffective on Itararé sandstone, mainly due to its mineralogical components, as the product does not adhere to quartz. When applied on Itaquera granite, the 1% TiO2 (w/v) concentration proved to be an appropriate treatment, as it demonstrated better thermal shock resistance, photocatalytic activity, porosity maintenance, and global colour when compared to the 4% concentration.

Photocatalytic degradation of dyes using rutile TiO2 synthesized by reverse micelle and low temperature methods: real-time monitoring of the degradation kinetics

The study proposes two new TiO2 photocatalysts with excellent photocatalytic properties obtained by the reverse micelle (RM-TiO2) and low temperature (LT-TiO2) methods. The crystal structure and morphology of the obtained TiO2 samples were analyzed by X-ray diffraction, scanning electron microscopy and IR-spectroscopy. The chosen synthesis conditions lead to pure rutile modification. FTIR spectra of the obtained samples contain characteristic bands, attributed to stretching vibrations of Ti–O bonds and to deformation vibrations of Ti–OH bonds. The average crystallite sizes for RM-TiO2 and LT-TiO2 samples are 5.4 and 9 nm, respectively. SEM analysis showed that the RM-TiO2 consists of TiO2 particles, assembled into spherical aggregates, while LT-TiO2 consists of smaller aggregates and is mostly mesoporous. The BET surface areas of the RM-TiO2 and LT-TiO2 samples are 39 and 63 m2/g, respectively. The photocatalytic degradation of the Congo Red (CR), Methyl Orange (MO) and Direct Red 23 (DR23) dyes in water medium has been studied under UV LED irradiation with H2O2 as an auxiliary oxidant. Both the RM-TiO2 and LT-TiO2 samples are active photocatalysts. The optimal dosages are 1.5 and 0.5 g/L respectively. The maximum photodegradation efficiency of RM-TiO2 is observed when the concentration of H2O2 is 15 mM for CR, 5 mM for MO and 10 mM for DR23. The maximum photodegradation efficiency of LT-TiO2 is observed when the concentration of H2O2 is 10 mM for CR, 2.5 mM for MO and 1.5 mM for DR23. The boosting effect of H2O2 on the degradation efficiency can be explained by an increased generation of •OH radicals. The real-time monitoring of degradation kinetics has been performed using measurements of light reflected from TiO2 suspension. The proposed technique allows the use of small volume of solution and amount of photocatalyst. The synthesized rutile photocatalysts may be used for wastewater treatment.

Nanophotocatalytic treatment of seawater using TiO2 immobilized and suspension system under solar irradiation

Organic fouling in desalination plants is a crucial phenomenon resulting in the deterioration of nanofiltration/reverse osmosis filtration performance of membranes and salt-rejection characteristics. In this research, the efficiency of TiO2-suspension and TiO2-immobilized photocatalysis to pretreat seawater under natural solar irradiation has been investigated. The solar nanophotocatalytic performance was evaluated in terms of chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency from feed seawater. Modelling and optimization study was performed in TiO2 suspension system to determine the effect and optimum settings of input parameters such as pH of seawater, reaction time, TiO2 dosage, initial TOC of seawater, and airflow rate into the photoreactor. In a full factorial design, the photocatalytic efficiency of TiO2 nano-thin film immobilized on borosilicate glass tubes was assessed in terms of methanol − TiO2 ratio, nitric acid − TiO2 ratio and solar irradiation time. The optimum removal efficiency of TOC and COD removal in the immobilized system was determined as 51.98% and 57.25%, respectively, at the input factor setting: methanol- TiO2 ratio = 15: 1, nitric acid- TiO2 ratio = 6:1 and solar irradiation time = 120 min. The optimum organic degradation in suspension system was found to be: TOC removal = 73.47% and COD removal = 65.48%.

Biological activity of titania coating prepared with zirconium oxychloride and titania on zirconia surface

Zirconia is recognized as a promising dental implant material because of its good biocompatibility, sufficient mechanical strength, minimal ion release and aesthetic effects similar to natural teeth. However, the limitations of inert surface of zirconia affect the long-term efficacy of zirconia implants. To enhance the osseointegration of zirconia implants, titania (TiO2) coating is prepared on the zirconia surface by immersion in a mixed zirconium oxychloride (ZrOCl2) and TiO2 suspension in a water bath. The surface and longitudinal section morphology are observed by scanning electron microscopy (SEM). The chemical composition is evaluated through energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The roughness and hydrophilicity of zirconia surface are also examined. A three-point bending test is conducted on the samples to explore the effect of this surface treatment on the mechanical strength of zirconia. Vickers hardness measurements are performed to evaluate the gradient change of the longitudinal section of the zirconia substrate. The MC3T3-E1 cells are seeded on zirconia discs, and a LIVE/DEAD double-staining test is conducted to detect the cytotoxicity of the TiO2 coating. The cell morphology is studied through fluorescence microscope. The degrees of cell proliferation, mineralization and alkaline phosphatase (ALP) activity are calculated and compared. Detection of the mRNA expression of osteogenic differentiation-related markers is performed by RT-PCR. A TiO2 coating is generated on the zirconia surface and significantly improves the surface roughness and hydrophilicity while not adversely affecting the mechanical strength of zirconia. The hardness of the zirconia substrate shows a gradient change. The TiO2 coating can promote proliferation, spreading and osteogenic differentiation of MC3T3-E1 cells. These findings suggest that modifying the surface of zirconia with a TiO2 coating may have a favourable osteogenic effect.

Photocatalytic inactivation of dual- and mono-species biofilms by immobilized TiO2.

Biofilms formed by different bacterial species are likely to play key roles in photocatalytic resistance. This study aims to evaluate the efficacy of a photocatalytic immobilized nanotube system (TiO2-NT) (IS) and suspended nanoparticles (TiO2-NP) (SS) against mono- and dual-species biofilms developed by Gram-negative and Gram-positive strains. Two main factors were corroborated to significantly affect the biofilm resistance during photocatalytic inactivation, i.e., the biofilm-growth conditions and biofilm-forming surfaces. Gram-positive bacteria showed great photosensitivity when forming dual-species biofilms in comparison with the Gram-positive bacteria in single communities. When grown onto TiO2-NT (IS) surfaces for immobilized photocatalytic systems, mono- and dual-species biofilms did not exhibit differences in photocatalytic inactivation according to kinetic constant values (p>0.05) but led to a reduction of ca. 3-4 log10. However, TiO2-NT (IS) surfaces did affect biofilm colonization as the growth of mono-species biofilms of Gram-negative and Gram-positive bacteria is significantly (p≤0.05) favored compared to co-culturing; although, the photocatalytic inactivation rate did not show initial bacterial concentration dependence. The biofilm growth surface (which depends on the photocatalytic configuration) also favored resistance of mono-species biofilms of Gram-positive bacteria compared to that of Gram-negative in immobilized photocatalytic systems, but opposite behavior was confirmed with suspended TiO2 (p≤0.05). Successful efficacy of immobilized TiO2 for inactivation of mono- and dual-species biofilms was accomplished, making it feasible to transfer this technology into real scenarios in water treatment and food processing.

An engineering approach towards the design of an innovative compact photo-reactor for antibiotic removal in the frame of laboratory and pilot-plant scale

Advanced Oxidation Processes (AOPs), in particular heterogeneous photocatalysis, have been considered as a promising method to remove antibiotics without generating hazardous intermediates. In this work, an innovative compact photoreactor was designed and tested for the degradation of the antibiotic Flumequine. The system consisted of a textile woven from both luminous and photocatalytically active fibers. The luminous fibers consisted of LED-type optical fibers and the photocatalytic fibers consist of textile fibers impregnated with TiO2. This configuration allowed for optimization of contact between the catalyst, the pollutant, and the light source. The surface morphology, elemental composition and optical properties of this photo-active fabric were characterized by SEM-EDX and by irradiance measurements. The effectiveness of the luminous textile was compared with two conventional processes: suspended TiO2, and immobilized TiO2 on cellulosic paper. The specific degradation rate obtained with the light textile was 28 times higher than that observed with slurry photocatalytic reactor and 65 times higher than in the case of TiO2 supported on cellulosic paper. Luminous textile also showed efficient performance in terms of mineralization per Watt consumed with values exceeding 77 and 419 times than those obtained with suspended TiO2 and the cellulose paper, respectively. This new configuration also improved the compactness by 3 times compared to the cellulosic paper system. The Langmuir-Hinshelwood model showed that this optical fibers-based configuration reduced the mass transfer compared to the conventional TiO2 immobilization approaches. Additionally, the extrapolation of this process to pilot scale was successfully performed. The excellent performances in terms of degradation rate, mineralization per Watt consumed, compactness, energy consumption, and reusability make luminous textiles an attractive alternative to conventional photocatalytic reactors’ design for removal of antibiotics in water and wastewater.

Photocatalytic exoskeleton: Chitin nanofiber for retrievable and sustainable TiO2 carriers for the decomposition of various pollutants

Loading a photocatalytic TiO2 to organic carriers has been desired for volumetric TiO2 incorporation, facile retrieval, and sustainable utilization. Traditionally, suspended TiO2 nanoparticles or its thin film on two-dimensional substrate are popularly fabricated for pollutants decomposition without carriers; due to poor thermomechanical properties of the organic carriers. Herein, a combination of the chitin nanofiber carrier and atomic layer deposition proves relevance for formation of anatase TiO2 thin layer so that photocatalytic decomposition in three-dimensional surface. Moreover, chitin nanofiber is capable of holding the TiO2 nanoparticles for multiple cycles of photocatalysis. Those types of TiO2 show characteristic degradation performance for gaseous (acetaldehyde) and aqueous pollutants (4-chlorophenol and rhodamine B). After catalytic reaction, chitin/TiO2 is retrievable owing to carrier's robustness even in water without TiO2 aggregation and loss. This work suggests that chitin-based photocatalyst is applicable to numerous pollutants through chitin's relatively high chemical resistance and stably wedged TiO2 during photocatalytic reaction.

Formaldehyde Analysis in Non-Aqueous Methanol Solutions by Infrared Spectroscopy and Electrospray Ionization.

We present the analysis of formaldehyde (HCHO) in anhydrous methanol (CH3OH) as a case study to quantify HCHO in non-aqueous samples. At higher concentrations (C > 0.07 M), we detect a product of HCHO, methoxy methanol (MM, CH3OCH2OH), by Fourier transform infrared spectroscopy, FTIR. Formaldehyde reacts with CH3OH, CD3OH, and CD3OD as shown by FTIR with a characteristic spectral feature around 1,195 cm−1 for CH3OH used for the qualitative detection of MM, a formaldehyde derivative in neat methanol. Ab initio calculations support this assignment. The extinction coefficient for 1,195 cm−1 is in the order of 1.4 × 102 M−1cm−1, which makes the detection limit by FTIR in the order of 0.07 M. For lower concentrations, we performed the quantitative analysis of non-aqueous samples by derivatization with dinitrophenylhydrazine (DNPH). The derivatization uses an aqueous H2SO4 solution to yield the formaldehyde derivatized hydrazone. Ba(OH)2 removes sulfate ions from the derivatized samples and a final extraction with isobutyl acetate to yield a 1:1 methanol: isobutyl acetate solvent for injection for electrospray ionization (ESI). The ESI analysis gave a linear calibration curve for concentrations from 10 to 200 µM with a time-of-flight analyzer (TOF). The detection and quantification limits are 7.8 and 26 μM, respectively, for a linear correlation with R 2 > 0.99. We propose that the formaldehyde in CH3OH is in equilibrium with the MM species, without evidence of HCHO in solution. In the presence of water, the peaks for MM become less resolved, as expected from the well-known equilibria of HCHO that favors the formation of methylene glycol and polymeric species. Our results show that HCHO, in methanol does not exist in the aldehyde form as the main chemical species. Still, HCHO is in equilibrium between the production of MM and the formation of hydrated species in the presence of water. We demonstrate the ESI-MS analysis of HCHO from a non-aqueous TiO2 suspension in methanol. Detection of HCHO after illumination of the colloid indicates that methanol photooxidation yields formaldehyde in equilibrium with the solvent.