Photodegradation Of Formaldehyde Research Articles

Photocatalytic Cleavage of C–H Bonds: A Case Study of Formaldehyde Photodegradation from Density Functional Theory

Photocatalytic Cleavage of C–H Bonds: A Case Study of Formaldehyde Photodegradation from Density Functional Theory

G-C3N4/TiO2 for gas-phase formaldehyde photodegradation under visible light in the humidity control coatings

BackgroundsThe control of relative humidity and degradation of volatile organic compounds are regarded as major considerations in the enhancement of living quality in the indoor environment. From the viewpoints of circular economy, the valorization of inorganic wastes to prepare green building materials is crucial. MethodsFor the practical applications, the multifunctional coatings, applied in the indoor humidity control and photocatalytic degradation of formaldehyde, are prepared by recovering inorganic wastes (i.e., white carbon (WC) and spent fluid catalytic cracking catalysts (sFCCC)) and photocatalysts (graphitic carbon nitride/TiO2, denoted as GCN/TiO2) via a simple sol-gel method. Various physicochemical and analytic tools are used to characterize the coating properties and performance. Significant findingsCompared to commercial coatings, the prepared multifunctional coatings (i.e., W/B/S-47/47/6, where W, B and S represent the weight percentage (%) of white carbon, bassanite and sFCCC, respectively) have superior textural properties which can improve the buffering ability of indoor humidity. Moreover, the W/B/S-47/47/6 coatings exhibit the surpassing photodegradation of formaldehyde over commercial coatings by ca. 3 times. The higher charge transfer kinetics and greater thermodynamic driving force toward superoxide radical formation are responsible for the improved photocatalytic activity of W/B/S-47/47/6 coatings. According to the toxicity characteristic leaching procedure tests, no evident leaching heavy metals are observed, which provides an environmental-friendly and economical route for valorization of inorganic wastes.

Supercritical carbon dioxide-assisted TiO2/g-C3N4 heterostructures tuning for efficient interfacial charge transfer and formaldehyde photo-degradation

Long exposure to formaldehyde has been a concern for causing respiratory problems and TiO2/g-C3N4 composite is a potential choice to address this issue. This study developed a supercritical carbon dioxide (ScCO2)-assisted method to fabricate TiO2/g-C3N4 composites with two distinct heterostructures. The g-C3N4 nanosheet/TiO2 nanoparticle (denoted as type 1 heterostructure) heterojunction could accelerate electron migration because of its large interfacial surface contact. The ternary TiO2{101}/g-C3N4/TiO2{001} heterojunction (denoted as type 2 heterostructure) was synthesized for the first time, further promoting the separation of photogenerated electron/hole pairs under full-spectrum irradiation because it provided an additional migration channel for photocarriers. By loading different amounts of TiO2, the heterostructures were modulated, thereby influencing the photoactivity of the composites. The TiO2/g-C3N4 composite with 58% TiO2 loading possessed the best photocatalytic performance, achieving the highest rate constant for formaldehyde degradation, approximately 7 times higher than pure bulk g-C3N4 under either visible or full-spectrum light. Under full-spectrum irradiation, the maximum decomposition rate approached nearly 100% within 90 min. The tuned heterostructures facilitated the generation of O2·− and·OH, which were dominant active oxygen radicals responsible for formaldehyde removal under light irradiation. Thus, this study developed a green route to synthesize composites with tunable heterojunctions and enhanced photocatalytic activity that can be used for indoor air pollutant degradation.

Silica wastes derived multifunctional coatings for formaldehyde photodegradation and autonomous indoor humidity buffering

To maintain a comfortable and healthy indoor environment without large amounts of energy consumption is of great importance. The progress of multifunctional indoor coatings with formaldehyde photodegradation and humidity buffering capability is necessary. From the viewpoints of circular economy, the preparation of effective photocatalysts (denoted as sFCC/GCN-x and ESF/GCN-y) via the decoration of recycling industrial wastes (i.e., spent fluid catalytic cracking catalysts (sFCC) and enhancement silica fume (ESF)) onto graphitic carbon nitride (GCN) by using a simple route is reported. The obtained results show that the prepared sFCC/GCN-0.15 and ESF/GCN-0.15 photocatalysts have the rate constants of formaldehyde degradation of 0.0075 and 0.0082 min−1, respectively, which are superior to that of pristine GCN (0.0044 min−1) under visible-light irradiation. The enhanced transfer kinetics of photogenerated electrons and declined recombination of electron-hole pairs may account for the surpassing photocatalytic performance. Results obtained from electron paramagnetic resonance spectra and Mott-Schottky plots indicate that the formation of ･O2− via the reaction of O2 with electrons generated on the conduction band is the major reaction pathway to photodegrade formaldehyde under visible light. To further assess the real applications of prepared photocatalysts, the sFCC/GCN-0.15 and ESF/GCN-0.15 are used to fabricate the multifunctional coatings (denoted as s- and E-coatings) with sFCC and ESF as the main compositions. Experimentally, the E-coatings could reach the formaldehyde degradation efficiency of ca. 84.5% after 3 h of visible light irradiation and excellent humidity buffering ability (293.8 g m−2) which is at least 10-folds higher than commercial coatings (28.9 g m−2). This notable progress of humidity buffering capacity on E-coatings can be attributed to their surface textural properties. Most importantly, this study exemplifies the valorization of inorganic silica wastes to produce sustainable and multifunctional coatings which may offer the practical and cost-effective applications in the indoor living space.

Effect of Calcination Temperature on Surface Acidity and Photocatalytic Activity of Nano-TiO2/Diatomite Composite Photocatalyst

Nano-TiO2/diatomite composite photocatalysts were prepared by hydrolysis-deposition method in the present study. The effect of calcination temperature on surface acidity and photocatalytic activity of the photocatalysts was characterized by X-ray diffraction, N2 adsorption/desorption, Fransmission electron microscope, Fourier transform infrared, X-ray photoelectron spectroscopy, pyridine adsorption in situ fourier transform infrared and the adsorption and photodegradation of formaldehyde in air. Results revealed that the high temperature and the nucleation of titanium dioxide both can consume the surface Brönsted acid sites, and with the formation of Ti–O–Si bond to form surface Lewis acid. The composite calcined at 600 °C presents the highest decomposition of formaldehyde under UV irradiation at the room temperature.

TiO2-WO3 Loaded onto Wood Surface for Photocatalytic Degradation of Formaldehyde

In this work, a facile method was adopted to prepare TiO2-WO3 loaded onto a wood surface by a two-step hydrothermal method. The as-prepared wood composite material can be used as a photocatalyst under UV irradiation for the photodegradation of formaldehyde. Related tests showed that TiO2-WO3 nano-architectonic materials with spherical particles loaded onto the wood substratewere mainly caused by self-photodegradation of formaldehyde. The TiO2-WO3 nanostructured material firmly adheres to the wood substrate through electrostatic and hydrogen bonding interactions. Meanwhile, the appearance of the new chemical bond Ti-O-W indicates the successful loading of TiO2-WO3 onto the wood surface. The photodegradation rate was measured and it was confirmed that the highest photodegradation performance of the modified wood was achieved at a molar ratio of 5:1 of TiO2 to WO3. This work provides a new strategy for the preparing of novel photocatalysts based on wood substrate. Moreover, the wood loaded with TiO2-WO3 is a promising candidate for indoor formaldehyde treatment in practical applications.

Nanoflower-like BiOBr/TiO2 p-n heterojunction composites for enhanced photodegradation of formaldehyde and dyes

A nanoflower-like BiOBr/TiO 2 p-n heterojunction photocatalyst was constructed and the possible photocatalytic mechanism was proposed. The construction of BiOBr/TiO 2 p-n heterojunction can significantly enhance the degradation of methyl orange (MO) and gaseous formaldehyde (HCHO) by photocatalysts. • A efficient nanoflower-like p-n heterojunction photocatalyst BiOBr/TiO 2 was prepared by simple solution coprecipitation. • This catalyst has enhanced photocatalytic degradation of dyes and formaldehyde. • P-n heterojunction effectively separates photogenerated carriers of BiOBr, hindering recombination of electrons and holes. The fabrication of p-n heterojunction is a smart strategy to improve the photocatalytic activity, because p-n junction can effectively promote the separation of photogenerated charges and improve the photocatalytic performance. Herein, a low cost nanoflower-like p-n heterojunction photocatalyst BiOBr/TiO 2 (abbreviated as BT-x) was prepared by simple solution coprecipitation method. Under visible light, BiOBr/TiO 2 p-n heterojunction photocatalyst showed enhanced photocatalytic activity in the degradation of Methyl Orange (MO) and gaseous formaldehyde (HCHO). The degradation rates of MO and HCHO by optimized composite BT-0.6 were 97% and 60% respectively. The p-type BiOBr with narrow band gap can effectively improve the visible light absorption, and its p-n heterojunction with TiO 2 can significantly improve the separation efficiency and transfer rate of photogenerated electron hole pairs. Meanwhile, multi-dimensional nanoflower structure is not only conducive to light reflection and improve light utilization, but also can expose more catalytic active sites. This p-n heterojunction composite material can be used as a new and promising catalyst for environmental applications.

A TiO2/polyurethane Composite for Photodegradation of Formaldehyde via Covalently Incorporation of Amino-functionalized TiO2

In this study, a TiO2/polyurethane composite (PU-TiO2) for photodegradation of formaldehyde was prepared based on TiO2 amino-functionalized with 3-aminopropyltriethoxysilane (APTS). FTIR, XPS, TG and TEM measurements demonstrated the successful amino-functionalization of TiO2 by APTS. Then the NH2-TiO2 were incorporated into polyurethane (PU) through urea linkages, and the thermal stability, mechanical properties as well as degradation efficiency of PU-TiO2 were investigated. PU-TiO2 possessed good thermal stability both in the storage and application. Compared with PU physically blended with TiO2, PU-TiO2 showed improved compatibility between PU and NH2-TiO2, evidenced by the enhanced mechanical properties. Most importantly, PU- TiO2 presented a good photoactivity for the degradation of formaldehyde.

Mn2+ doped AgInS2 photocatalyst for formaldehyde degradation and hydrogen production from water splitting by carbon tube enhancement

In this work, AgInS2 and Mn2+ doped AgInS2 (Mn-AgInS2) with different Mn2+: (Ag++In3+) ratios were synthesized via a low temperature liquid method. The photocatalytic activity of the obtained samples was followed by taking formaldehyde as the target pollutant under visible light irradiation. The photocatalysts were passed through various characterization procedures to investigate their morphological, structural and photophysical characteristics. The optimal proportion sample [with the ratio n (Mn2+): n (Ag++In3+)=1:100] photodegraded about 79% formaldehyde in 150min. These upgraded activities are attributed to the enhanced visible light absorption and superior charge separation due to the presence of Mn2+ as confirmed site from charge separation measurements. In addition, a possible mechanism for the photodegradation of formaldehyde is proposed based on the experimental results. Furthermore, the photocatalytic water splitting performance of Mn-AgInS2 and multi-walled carbon nanotubes (MWCNTs) modified Mn-AgInS2 is investigated and compared under simulated sunlight irradiation, and remarkable hydrogen production is achieved (105μmolh-1 g-1) by using the latter.

Flower-like ZnO/BiOI p–n heterojunction composites for enhanced photodegradation of formaldehyde and dyes

Flower-like ZnO/BiOI p–n heterojunction composites for enhanced photodegradation of formaldehyde and dyes

A two-step nonthermal plasma method to fabricate Ag/N- doped TiO2/CNTs for formaldehyde removal under visible light irradiation

A novel efficient catalyst called Ag/N-doped TiO2/CNTs was fabricated using a two-step method involving treatment with ammonia plasma followed by a process of hydrogen plasma reduction at a low temperature. The photocatalyst, which was composed of silver nanoparticles (AgNPs), titanium dioxide (TiO2) and 5% amount of carbon nanotubes (CNTs), achieved an adequate formaldehyde elimination rate of 95% under visible-light irradiation. A series of analytical methods was employed to investigate the advantages of the novel fabrication method. The results showed that the first step, which is the N doping of TiO2 could be particularly important for improving the photocatalytic performance because of the reduced band gap and newly formed Ti3+. Furthermore, it could assist in the anchor of AgNPs during the second step of fabrication. During the second step of hydrogen reduction process, AgNPs of smaller sizes were more homogeneously anchored on the surface of N-doped TiO2/CNTs than that of the catalysts without ammonia plasma treatment. The resulting higher level of AgNPs could aid in efficient electron transfer and significantly improve the response to visible light, considering the surface plasmon resonance effect. CNTs and AgNPs played significant roles as electron acceptors in reducing the recombination rate of photogenerated hole pairs, and moreover, this two-step plasma process could be beneficial for achieving surface and interface properties suitable for formaldehyde photodegradation. This novel approach for fabricating an efficient Ag/N-doped TiO2/CNTs has potential for application in environmental purification systems.

Synergistic effect of diatomite and Bi self-doping Bi2MoO6 on visible light photodegradation of formaldehyde

Good indoor air environment is of great significance for the health and comfort assurance of occupants. In this work, a series of bismuth self-doping Bi 2 MoO 6 /diatomite (BD-X) composites with different proportions of bismuth and molybdenum source were prepared via a mild solvothermal process. Under visible light irradiation, the BD-3 sample exhibited the optimal formaldehyde (HCHO) mineralization performance, and the corresponding calculated rate constant was up to 3.2 times higher than that of bare Bi 2 MoO 6 (B). The introduction of diatomite as catalyst carrier could not only contribute to the dispersion of nano-scale Bi 2 MoO 6 photocatalyst, but also promote the exposure of (001) crystal plane of Bi 2 MoO 6 . In particular, the molybdenum vacancy generated with increasing the proportion of bismuth source, which effectively facilitated the separation of photogenerated carriers. Moreover, the photogenerated holes (h + ) played the major role in the photocatalytic degradation process. Overall, this research would provide a novel binary composite photocatalyst derived from natural mineral for the high-efficient mineralization of formaldehyde under visible light. • An efficient adsorption-photocatalysis system was constructed with diatomite as carrier. • The molybdenum vacancy generated with increasing the proportion of bismuth source. • Diatomite and Bi self-doping Bi 2 MoO 6 promoted the synergistic photodegradation of HCHO. • Excellent photocatalytic mineralization of HCHO was obtained under visible light.

Enhanced visible-light properties of TiO2/diatomite composite over varied bismuth semiconductors modification for formaldehyde photodegradation: A comparative study

How to improve the photocatalytic performance of titania-based photocatalyst under visible light in environmental remediation remains a challenge. Herein, three kinds of bismuth semiconductors, including Bi2MoO6, BiOCl and BiVO4, are selected to construct heterojunctions with diatomite supporting titania for improving photocatalytic performance towards formaldehyde (HCHO) under visible light. The morphologies and microstructures as well as the photocatalytic performance of the as-received samples are systematically investigated for comparation. The Bi2MoO6-TiO2/diatomite (MTD-50) composite has the optimal performance, followed by BiOCl-TiO2/diatomite (CTD-100) composite and BiVO4-TiO2/diatomite (VTD-75) composite, whose mineralization rate is up to around 47.58 times, 29.55 times and 21.14 times that of TiO2/diatomite (TD) composite, respectively. Moreover, the performance enhancement mechanism could be attributed to their relatively high quantum efficiency that originated from the heterojunctions, resulting in the high generation efficiency of active radicals. This work would like to compare bismuth semiconductor photocatalysts for enhancing visible-light properties through heterojunction and provide comparative references for developing novel visible light driven photocatalysts in the field of indoor HCHO purification.

Using formaldehyde as a novel chemical actinometer for 185 nm vacuum ultraviolet photon flux quantification in water

Quantifying ultraviolet (UV) photon flux is important for water photolysis practice. However, it is currently challenging to quantify the photon flux of 185 nm vacuum UV (VUV185) emitted by low-pressure mercury lamp (LPML) because of the interference of coexisting 254 nm UV (UV254). Given that formaldehyde (FA) is insensitive to UV254 within the time scale of interests whereas vulnerable to VUV185, this study for the first time evaluated the possibility of using FA as a chemical actinometer to determine the VUV185 photon flux under varying conditions. Experimental results revealed that the photodegradation of FA followed a pseudo-1st-order reaction kinetic under VUV185 irradiation, and the products of initial concentration (C0) and reaction rate constants (i.e., C0 × k) were proportional to the numbers of LPMLs (under C0 of 50–300 mg/L), suggesting that C0 × k is an excellent indicator for photon flux determination. Increasing dissolved oxygen concentration from 1.0 to 7.8 mg/L, pH from 4.0 to 10.4, and temperature from 22 to 44 °C all imposed negligible interferences (variation ≤ 10%) on the C0 × k values, proving that FA is a good actinometer for VUV185 photon flux detection. Because FA can be measured readily by spectrophotometry method, its use as an actinometer is more convenient than conventional actinometers. Therefore, this study demonstrates that FA is a promising candidate of actinometer for VUV185 quantification in the copresence of UV254.

Size-Controlled C/N-Doped TiO<sub>2</sub> Nanoparticles for Visible-Light-Driven Photocatalysis of Formaldehyde from Plywood

We reported a facile solvothermal approach to synthesize C/N-doped TiO2 (C/N-T) using a template-free method. The morphology and composition of the C/N-T were evaluated by transmission electron microscopy, X-ray diffraction, wavelength dispersive spectroscopy and X-ray photoelectron spectroscopy. The photodegradation of formaldehyde was studied in environmental chambers under specific conditions combined with UV-Vis determinations. The catalytic oxidations of C/N-T nanoparticles were characterized by degrading formaldehyde of plywood, which was induced via visible-light illumination. A maximum 95.7% of degradation efficiency within 55 min showed enhanced photocatalytic activity.

Hydrogenated Amorphous Titania with Engineered Surface Oxygen Vacancy for Efficient Formaldehyde and Dye Removals under Visible-Light Irradiation.

Hydrogenated crystalized TiO2−x with oxygen vacant (OV) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO2, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO2−x (HAm-TiO2−x) with engineered surface OV and high surface area (176.7 cm2 g−1) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO2−x, we found that OV was energetically retained in the subsurface region; in particular, the subsurface OV-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm2). Thus, HAm-TiO2−x achieved high quantum efficiency of 3 × 10−6 molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O2 (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO2−x are both largely promoted in the presence of subsurface OV. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.

Z-scheme K-C3N4/Ag/Ag3PMo12O40 heterojunction with improved visible light photodegradation of formaldehyde

Photocatalytic degradation of formaldehyde is an ideal way to solve indoor air pollution. The development of Z-scheme heterojunction photocatalysts is economic and effective way in eliminating formaldehyde pollution. Herein, a ternary heterojunction photocatalyst K-C3N4/Ag/Ag3PMo12O40 (abbreviated as K-C3N4/Ag/APM) was synthesized by self-assembly of PMo12O403- with Ag+ and K-C3N4 followed by in-situ photoreduction. The Ag/Ag3PMo12O40 (APM) hetero-nanoparticles obtained by photoreduction are uniformly loaded on K-C3N4 nanosheets. The structure, morphology, optical and photoelectrochemical properties etc. of K-C3N4/Ag/APM were characterized and explored. The photocatalytic activity of K-C3N4/Ag/APM was assessed on the degradation of HCHO. K-C3N4/Ag/APM showed remarkably improved photocatalytic activity than the g-C3N4, K-C3N4 and K-C3N4/Ag in the degradation of HCHO under visible light irradiation. The K-C3N4/Ag/APM heterojunction can degrade 60% gaseous HCHO (0.16 mg L-1) in 60 min (λ > 400 nm). The optimum experimental parameters were temperature 20 ℃, RH 70%, catalyst amount 20 mg and initial HCHO concentration 0.16 mg L-1. The enhanced photocatalytic efficiency of K-C3N4/Ag/APM is attributed to the synergistic effect of improved light harvesting, excellent interface contact and accelerated transmission and separation of photogenerated carriers in the Z-scheme structure with Ag as efficient electron transfer mediators. Free radical trapping and electron spin resonance (ESR) experiments confirmed the Z-scheme charge transfer mechanism, and proved that •O2– and h+ were the main active species in HCHO oxidation reaction. The intermediate species in the HCHO photocatalytic degradation process were tested by in situ DRIFTS technology. The construction of g-C3N4 based Z-scheme photocatalyst may provide an insight for the design of new and efficient photocatalysts for environmental applications.

Current perspectives of anodized TiO2 nanotubes towards photodegradation of formaldehyde: A short review

Recently, TiO 2 nanotubes (NTs) have gained enormous research interest and the quest to enhance their photocatalytic properties and performance for the gaseous pollutants’ removal, especially formaldehyde continues. Several synthetic routes have been adopted for fabrication of TiO 2 NTs. As the development in this area of research in nanotechnology nowhere seems to retard with increasing concerns due to the presence of toxic formaldehyde in indoor environment, the fabrication or synthesis approaches for growing TiO 2 NTs are becoming more relevant than ever. In that aspect there is a dire need for critical assessment of the current perspective on synthesis routes and their ability to present a solution for the primary challenges of utilizing toxic solvents and expensive fabrication procedures and facilities. The present review gives a meaningful insight into the fabrication routes for TiO2 NTs and highlighting the key finding from previous studies, thereby identifying the core challenges and strength of existing techniques. The state of the art is elaborated along with an all-inclusive review on the mechanism of nanotubes formation and photodegradation of formaldehyde by TiO 2 NTs. A group of emerging ionic-liquid based electrolytes known as deep eutectic solvents for TiO2 NTs fabrication were identified as the potential electrolytes to overcome the limitations of the existing methods. Conclusive research needs in the above mentioned aspects are suggested accordingly.

Synthesis of submicron-sized carbon-doped TiO2 for photodegradation of formaldehyde from wood-based panels

Carbon-doped TiO2 particles were prepared by hydrothermal treatments and characterised via field emission scanning electron microscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy. The results show that carbon was successfully doped into the TiO2 structures. Photocatalytic reactions were further investigated in a simulated indoor environment, and the visible-light catalytic activity of the carbon-doped TiO2 was evaluated by monitoring the photodegradation of the formaldehyde from wood-based panels. A degradation rate of 90% in 70 min was obtained, which demonstrated high photocatalytic performance.

Design and Synthesis of Microencapsulated Phase-Change Materials with a Poly(divinylbenzene)/Dioxide Titanium Hybrid Shell for Energy Storage and Formaldehyde Photodegradation

A novel series of microcapsules with high thermal energy storage (TES) and formaldehyde photodegradation functions was successfully fabricated by eco-friendly Pickering emulsion polymerization with...