Coupling of titania with multiwall carbon nanotubes for decomposition of gas-phase pollutants under simulated indoor conditions

This study synthesized multiwall carbon nanotube (MWNT)–titania (TiO₂) composites and examined their characteristics and photocatalytic performance for the cleaning of gas-phase benzene, toluene, ethyl benzene, and o-xylene (BTEX) under simulated indoor conditions. Optical and spectral surveys of the as-synthesized composite confirmed that the TiO₂ nanoparticles were bound intimately to the MWNT networks. The photocatalytic performance was evaluated using an annular-type reactor inner-coated with MWNT–TiO₂ or Degussa P25 TiO₂. The composite revealed gas removal ability superior to that of stand-alone TiO₂. This composite was also less affected by humidity during toluene decomposition compared to the previous result obtained from a stand-alone TiO₂. Unlike another previous result obtained from the TiO₂, the performance of the composite was not affected by changes in input concentration (IC) within a simulated indoor air quality range (0.1–1.0 ppm) but it decreased significantly when the IC was increased to 5 and 10 ppm. As the flow rate was decreased from 4.0 to 1.0 L min^?1, the average efficiency for the target compounds increased to 95% or ～100%. The MWNT–TiO₂ composite could be applied effectively to the decomposition for BTEX under certain simulated indoor conditions.

Implications: Unlike water applications, there are few reports of gas-phase applications of multiwall carbon nanotubes (MWCNT)–TiO₂ composites. This study found that MWCNT–TiO₂ composites showed performance in the removal of toxic gaseous aromatic superior to that of stand-alone TiO₂. In addition, the pollutant degradation efficiency of the composite was less affected by humidity than for a stand-alone TiO₂ unit within a simulated indoor relative humidity range. Moreover, unlike the TiO₂ unit, the composite's performance was not affected by variations in the input concentrations within the simulated indoor air quality (IAQ) range. In addition, the decomposition efficiencies increased to 100% with decreasing flow rate.     

可见光活性纳米TiO2光催化涂料的抗菌性能研究

基于过渡金属离子掺杂技术,制备了在室内光辐照条件下具有良好光催化抗菌性能的可见光响应型铁掺杂TiO2光催化涂料.研究结果表明,在可见光活性光催化涂料中添加1%的纳米TiO2时,抗菌效果最好,光照24 h后对大肠杆菌、白色念珠球菌、黑曲霉的杀菌率分别达到99.9%、97.2%、82%.采用致孔剂聚乙二醇6 000对光催化...     

Fouling mitigation and cleanability of TiO<Subscript>2</Subscript> photocatalyst-modified PVDF membranes during ultrafiltration of model oily wastewater with different salt contents

In the present study, TiO₂-coated ultrafiltration membranes were prepared and used for oily water filtration (droplet size <?2 μm). The aim of this work was to investigate the effect of different salt contents on fouling and filtration properties of neat and TiO₂-coated membranes during oil-in-water emulsion filtration. The effect of the TiO₂ coating on the flux, surface free energy, and retention values was measured and compared with the neat membrane values. The cleanability of the fouled TiO₂-coated membranes by UV irradiation was also investigated by measuring flux recovery and contact angles, and the chemical changes during cleaning were characterized by ATR-IR. It was found that increasing the salt content of the model wastewaters, oil-in-water emulsions, increased the zeta potential and the size of the droplets. The presence of the TiO₂ coating decreases the membrane fouling during oily emulsion filtration compared to the neat membrane, due to the hydrophilicity of the coating regardless of the salt content of the emulsions. The neat and coated membrane oil retention was similar, 96?±?2%. The coated membrane can be effectively cleaned with UV irradiation without additional chemicals and a significant flux recovery can be achieved. Monitoring of the cleaning process by following the membrane surface wettability and ATR-IR measurements showed that the recovery of flux does not mean the total elimination of the oil layer from the membrane surface.     

Adsorption and photocatalytic decomposition of roxarsone by TiO2 and its mechanism

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been widely used as organic arsenic additive in animal industry. In this study, the adsorption of roxarsone on TiO₂ under dark conditions, the photocatalytic decomposition of roxarsone under UV/TiO₂, and the possible photocatalytic pathway were investigated. At the initial concentration of 5–35 mg/L, the adsorption of roxarsone fitted well with the pseudo-second-order kinetics. The isotherms analysis showed that the Langmuir model was better than the Freundlich and Dubinin–Radushkevich models for describing the adsorption process. After 7 h of photocatalytic decomposition, a complete disappearance of roxarsone was achieved. The pH value has a significant effect on both adsorption and photocatalytic decomposition of roxarsone. The results of high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) and gas chromatography-mass spectrometry (GC/MS) analyses proved the cleavage of the As-C bond during the photocatalytic decomposition process by TiO₂ and the intermediates of the decomposition. Based on the results, a possible photocatalytic decomposition pathway was proposed.     

Cu/La共掺杂TiO2光催化氧化水中的氨氮

采用水解-沉淀法制备了Cu/La共掺杂纳米TiO2催化剂,利用XRD、XPS和BET技术对其进行表征,并考察了在紫外灯下,共掺杂TiO2对氨氮的光催化氧化工艺条件。物相结构和比表面积测试结果表明,共掺杂催化剂具有较好的锐钛矿晶型,孔径分布为4～8 nm,Cu/La共掺杂TiO2La以La3+,Cu是以Cu2+、Cu+的形式掺杂进入TiO2的晶格。光催化实验表明:所得改性光催化剂对氨氮的去除及焦化废水的处理均具有较高的催化活性。     

Antifungal efficiency assessment of the TiO2 coating on façade paints

The work studies the photocatalytic activity and the antifungal efficiency of the TiO₂/Zn-Al coatings placed on the target commercial façade paints. The photocatalytic active nanocomposite based on TiO₂ and Zn-Al-layered double hydroxides (ZnAl-LDHs) was synthesized by a wet impregnation technique with 3 % w/w TiO₂. The freshly prepared suspension was applied by spray technique on the surfaces of the white façade paints. The goal of the work was to develop a method that quickly quantifies the antifungal activity of the commercial façade paints with and without biocidal components covered with a photocatalytic coating. The essence of the proposed method is the monitoring of the fungal growth (artificial ageing conditions) and the quantification of its development (UV-A 0.13 mWcm^?2) on the façade paint surfaces. A special fungus nutrient (potato dextrose agar (PDA)) was inoculated with the spores of the Aspergillus niger ATCC 6275, and the test samples (façade paints with and without photocatalytic coating) were placed on the inoculated nutrient in the petri dishes. The images of the fungal growth on the samples of the facade paints, during a period of 5 days, were imported into Matlab R2012a where they were converted to binary images (BW), based on the adequate threshold. The percentage of the surface coverage was calculated by applying the specifically written program code which determines the ratio of the black and white pixels. The black pixels correspond to the surface covered with hyphae and mycelia of the fungus.     

Photodegradation of gaseous acetaldehyde and methylene blue in aqueous solution with titanium dioxide-loaded activated carbon fiber polymer materials and aquatic plant ecotoxicity tests

TiO₂-supported activated carbon felts (TiO₂–ACFTs) were prepared by dip coating of felts composed of activated carbon fibers (ACFs) with either polyester fibers (PS-A20) and/or a polyethylene pulp (PE-W15) in a TiO₂ aqueous suspension followed by calcination at 250 °C for 1 h. The as-prepared TiO₂–ACFTs with 29–35 wt.% TiO₂ were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ adsorption. The TiO₂–ACFT(PS-A20) samples with 0 and 29 wt.% TiO₂ were microporous with specific surface areas (S _BET) of 996 and 738 m²/g, respectively, whereas the TiO₂–ACFT(PE-W15) samples with 0 and 35 wt.% TiO₂ were mesoporous with S _BET of 826 and 586 m²/g, respectively. Adsorption and photocatalytic activity of the as-prepared samples were evaluated by measuring adsorption in the dark and photodegradation of gaseous acetaldehyde (AcH) and methylene blue (MB) in aqueous solution under UV light. The TiO₂ loading caused a considerable decrease in the S _BET and MB adsorption capacity along with an increase in MB photodegradation and AcH mineralization. Lemna minor was chosen as a representative aquatic plant for ecotoxicity tests measuring detoxification of water obtained from the MB photodegradation reaction with the TiO₂–ACFT samples under UV light.     

Adsorptive removal and photocatalytic decomposition of sulfamethazine in secondary effluent using TiO2–zeolite composites

We investigated the adsorption and decomposition of sulfamethazine (SMT), which is used as a synthetic antibacterial agent and discharged into environmental water, using high-silica Y-type zeolite (HSZ-385), titanium dioxide (TiO₂), and TiO₂–zeolite composites. By using ultrapure water and secondary effluent as solvents, we prepared SMT solutions (10 μg/L and 10 mg/L) and used them for adsorption and photocatalytic decomposition experiments. When HSZ-385 was used as an adsorbent, rapid adsorption of SMT in the secondary effluent was confirmed, and the adsorption reached equilibrium within 10 min. The photocatalytic decomposition rate using TiO₂ in the secondary effluent was lower than that in ultrapure water, and we clarified the inhibitory effect of ions and organic matter contained in the secondary effluent on the reaction. We synthesized TiO₂–zeolite composites and applied them to the removal of SMT. During the treatment of 10 μg/L SMT in the secondary effluent using the composites, 76 % and more than 99 % of the SMT were decomposed within 2 and 4 h by photocatalysis. The SMT was selectively adsorbed onto high-silica Y-type zeolite in the composites. Resultantly, the inhibitory effect of the coexisting materials was reduced, and the composites could remove SMT more effectively compared with TiO₂ alone in the secondary effluent.     

CNTs/TiO2/CS光降解苯的动力学

综合光催化氧化苯的动力学过程、光辐射场模型和质量守恒定律,采用平板型反应器建立了碳纳米管/二氧化钛/壳聚糖(CNTs/TiO2/CS)催化薄膜光催化氧化气相苯的数学模型;该模型考虑了光强、相对湿度、初始浓度与气体流速对气相苯光降解的影响。结果表明,建立的数学模型与实验结果吻合较好。     

Photocatalytic decomposition of methanol over La/TiO<Subscript>2</Subscript> materials

Lanthanum-modified TiO₂ photocatalysts (0.2–1.5 wt% La) were investigated in the methanol decomposition in an aqueous solution. The photocatalysts were prepared by the common sol-gel method followed by calcination. The structural (X-ray diffraction, Raman, X-ray photoelectron spectroscopy), textural (N₂ physisorption), and optical properties (diffuse reflectance spectroscopy, photoelectrochemical measurements) of all synthetized nanomaterials were correlated with photocatalytic activity. Both pure TiO₂ and La-doped TiO₂ photocatalysts proved higher yields of hydrogen in comparison to photolysis. The photocatalyst with optimal amount of lanthanum (0.2 wt% La) showed almost two times higher amount of hydrogen produced at the same time as in the presence of pure TiO₂. The photocatalytic activity increased with both increasing photocurrent response and decreasing amount of lattice and surface O species. It has been shown that both direct and indirect mechanisms of methanol photocatalytic oxidation participate in the production of hydrogen. Both direct and indirect mechanisms take part in the formation of hydrogen.     

Investigation of the antibacterial effects of silver-modified TiO2 and ZnO plasmonic photocatalysts embedded in polymer thin films

Nanosilver-modified TiO₂ and ZnO photocatalysts were studied against methicillin-resistant Staphylococcus aureus on the surface and against naturally occurring airborne microorganisms. The photocatalysts/polymer nanohybrid films were prepared by spray coating technique on the surface of glass plates and on the inner surface of the reactive light source. The photoreactive surfaces were activated with visible light emitting LED light at λ?=?405 nm. The optical properties of the prepared photocatalyst/polymer nanohybrid films were characterized by diffuse reflectance measurements. The photocatalytic properties were verified with the degradation of ethanol by gas chromatography measurements. The destruction of the bacterial cell wall component was examined with transmission electron microscope. The antibacterial effect of the photocatalyst/polymer nanohybrid films was tested with different methods and with the associated standard ISO 27447:2009. With the photoreactive coatings, an extensive disinfectant film was developed and successfully prepared. The cell wall component of S. aureus was degraded after 1 h of illumination. The antibacterial effect of the nanohybrid films has been proven by measuring the decrease of the number of methicillin-resistant S. aureus on the surface and in the air as the function of illumination time. The photocatalyst/polymer nanohybrid films could inactivate 99.9 % of the investigated bacteria on different thin films after 2 h of illumination with visible light source. The reactive light source with the inner-coated photocatalyst could kill 96 % of naturally occurring airborne microorganisms after 48 h of visible light illumination in indoor air sample. The TEM results and the microbiological measurements were completed with toxicity tests carried out with Vibrio fischeri bioluminescence bacterium.     

CdS-TiO_2/MWCNTs结构表征及其光催化性能

采用溶胶-凝胶法,制备了多壁碳纳米管(MWCNTs)负载的双组分复合半导体光催化剂CdS-TiO2/MWCNTs。通过透射电镜(TEM)、比表面分析(BET)、X射线衍射(XRD)和紫外-可见吸收光谱(UV-vis)等分析方法对光催化剂进行了结构表征,并考察了CdS-TiO2/MWCNTs对甲苯降解的光催化性能。结果表明:纳米活性粒子CdS-TiO2均匀负载于MWCNTs上,比表面积、光吸收阈值和强度增大,活性粒子间以及活性粒子与载体之间具有协同作用,有利于光催化性能的提高,CdS-TiO2/MWCNTs在主波长为254 nm紫外光照射下对甲苯的降解效果较好,去除率可达55.3%。     

Photocatalytic degradation of acetaminophen in modified TiO2 under visible irradiation

This study investigated the photocatalytic degradation of acetaminophen (ACT) in synthetic titanium dioxide (TiO₂) solution under a visible light (λ >440 nm). The TiO₂ photocatalyst used in this study was synthesized via sol–gel method and doped with potassium aluminum sulfate (KAl(SO₄)₂) and sodium aluminate (NaAlO₂). The influence of some parameters on the degradation of acetaminophen was examined, such as initial pH, photocatalyst dosage, and initial ACT concentration. The optimal operational conditions were also determined. Results showed that synthetic TiO₂ catalysts presented mainly as anatase phase and no rutile phase was observed. The results of photocatalytic degradation showed that LED alone degraded negligible amount of ACT but with the presence of TiO₂/KAl(SO₄)₂, 95 % removal of 0.10-mM acetaminophen in 540-min irradiation time was achieved. The synthetic TiO₂/KAl(SO₄)₂ presented better photocatalytic degradation of acetaminophen than commercially available Degussa P-25. The weak crystallinity of synthesized TiO₂/NaAlO₂ photocatalyst showed low photocatalytic degradation than TiO₂/KAl(SO₄)₂. The optimal operational conditions were obtained in pH 6.9 with a dose of 1.0 g/L TiO₂/KAl(SO₄)₂ at 30 °C. Kinetic study illustrated that photocatalytic degradation of acetaminophen fits well in the pseudo-first order model. Competitive reactions from intermediates affected the degradation rate of ACT, and were more obvious as the initial ACT concentration increased.     

活性炭纤维负载TiO2光催化降解甲醛的影响因素

利用自制光催化气体反应器体系,以活性炭纤维负载TiO₂作催化剂,在紫外光照射下模拟降解室内污染气体甲醛,测试了活性炭纤维负载TiO₂催化剂的催化活性,探讨了紫外光光强、催化剂的酸度、反应器内湿度及反应时间等控制反应的主要因素对甲醛降解率的影响。结果表明,活性炭纤维与TiO₂的协同作用大大提高了对甲醛的降解效果;紫外光强增倍对甲醛降解率有一定提高,但提高幅度仅为11.71%;活性炭纤维用pH=5的TiO₂溶胶浸泡做催化剂对甲醛的降解效果最好,60 min内降解率达到68.37％;反应器内的湿度为81%甲醛降解率最高,反应60 min后达82.2%;随着反应时间的延长,甲醛降解率的上升幅度不断减小,最高只能达到94.59%。     

Synthesis of BiVO4/TiO2 composites and evaluation of their photocatalytic activity under indoor illumination

BiVO₄/TiO₂ composites with different weight ratios have been prepared by coprecipitation-based reactions followed by either thermal or hydrothermal treatment with the aim of evaluating the TiO₂ photosensitization by BiVO₄. The obtained materials present in all cases the desired monoclinic phase of BiVO₄ and anatase phase of TiO₂. Visible light absorption increased with increasing amount of bismuth vanadate. XPS results reveal the surface enrichment of Ti with respect to the bulk composition in samples characterised by a higher content of BiVO₄. The photocatalytic activity of the prepared materials was tested for the degradation of isopropanol in the gas phase under indoor illumination conditions. Although none of the composites was able to improve the activity of TiO₂, the low BiVO₄ containing samples appear as more suitable for further synthesis tuning.     

光催化降解模拟室内挥发性有机污染物研究

用浸渍-提拉法制备玻璃弹簧负载型TiO2薄膜催化剂,在自制的反应器中进行光催化降解由丙酮、甲苯、对二甲苯组成的模拟室内挥发性有机污染物VOCs研究.研究发现:催化剂中掺杂金属离子能影响催化剂的降解效果,降解效果依次为掺铈TiO2＞纯TiO2＞掺银TiO2;气体流量显著影响降解效果,丙酮、甲苯和对二甲苯的最佳降解流量分别为3、5、7 L/min;混合气体中非对称性的极性分子的降解效率高于对称性分子,导致丙酮、对二甲苯组分降解率降低,甲苯降解率增高.     

碳纳米管/二氧化钛/壳聚糖催化薄膜光催化活性及苯降解机理

通过X-射线衍射仪(XRD)、扫描电镜(SEM)、透射电镜(TEM)和紫外可见光漫反射谱(UV-vis)对碳纳米管/二氧化钛/壳聚糖复合薄膜的晶体结构和形貌进行表征,以室内空气典型污染物气相苯为模型反应物,研究碳纳米管/二氧化钛/壳聚糖催化薄膜的光催化活性及其对苯的光降解机理。结果表明,制备的碳纳米管/二氧化钛/壳聚糖催化薄膜所具有的良好催化活性归功于碳纳米管、二氧化钛和壳聚糖三者的协调效应;气相苯光降解产生的主要中间产物是乙酸乙酯和十一烷,以及少量的丙烯醛、4-羰基-甲基-苯乙酮、十二烷烃、2,4,-二叔丁基苯酚、二十一烷烃。根据红外光谱分析与GC/MS分析结果,进一步提出了气相苯的降解机理过程。     

铂铈共掺杂纳米TiO2的制备、表征及光催化性能

以钛酸四丁酯为前驱体,过氧化氢为氧化剂,采用简单易行的低温氧化法制备出晶粒尺寸较小(平均尺寸25 nm)的二氧化钛纳米粒子。通过贵金属Pt掺杂TiO₂(Pt-TiO₂)、稀土元素Ce掺杂TiO₂(Ce-TiO₂)和Pt、Ce共掺杂TiO₂(Pt/Ce-TiO₂)的掺杂的方法对二氧化钛进行改性。通过XRD,XPS,TEM,紫外漫反射等表征手段对制备的样品进行表征。通过可见光下降解罗丹明B来测试其光催化活性。实验结果表明,由Ce掺杂的TiO₂光催化剂对有机污染物的最大降解能力略大于Pt掺杂的TiO₂,2种元素进行共同掺杂时对应的TiO₂光催化剂降解能力最大。     

Photocatalytic ozonation of terephthalic acid: a by-product-oriented decomposition study

Terephthalic acid (TA) is considered as a refractory model compound. For this reason, the TA degradation usually requires a prolonged reaction time to achieve mineralization. In this study, vanadium oxide (V_xO_y) supported on titanium oxide (TiO₂) served as a photocatalyst in the ozonation of the TA with light-emitting diodes (LEDs), having a bandwidth centered at 452 nm. The modified catalyst (V_xO_y/TiO₂) in combination with ozone and LEDs improved the TA degradation and its by-products. The results obtained by this system were compared with photolysis, single ozonation, catalytic ozonation, and photocatalytic ozonation of V_xO_y/TiO₂ with UV lamp. The LED-based photocatalytic ozonation showed almost the same decomposition efficiency of the TA, but it was better in comparison with the use of UV lamp. The oxalic acid accumulation, as the final product of the TA decomposition, was directly influenced by either the presence of V_xO_y or/and the LED irradiation. Several by-products formed during the TA degradation, such as muconic, fumaric, and oxalic acids, were identified. Besides, two unidentified by-products were completely removed during the observed time (60 min). It was proposed that the TA elimination in the presence of V_xO_y/TiO₂ as catalyst was carried out by the combination of different mechanisms: molecular ozone reaction, indirect mechanism conducted by ·OH, and the surface complex formation.     

Relationship between Pd oxidation states on TiO2 and the photocatalytic oxidation behaviors of nitric oxide

This study has been undertaken to investigate the relationship between Pd oxidation states on TiO₂ photocatalysts and their photocatalytic oxidation behaviors of NO. Three types of Pd-modified TiO₂ with different Pd oxidation states were prepared by wet impregnation method, neutralization method and photodeposition method, respectively. And these Pd-modified photocatalysts were characterized by X-ray diffraction analysis, X-ray photoelectron spectrum analysis (XPS), UV–Vis diffuse reflectance spectra and temperature programmed desorption (TPD). It was found from XPS results that the dominant oxidation states of Pd on these Pd-modified TiO₂ catalysts were Pd²⁺, PdO, and Pd⁰, respectively. NO-TPD results showed that the NO adsorption capacity was improved greatly by the modification of Pd²⁺ ions. The activity tests showed that Pd-modified TiO₂ by a wet impregnation method increased photocatalytic activity compared to pure TiO₂ (Degussa P25). It was concluded that Pd²⁺ ions on as-prepared TiO₂ catalysts provided key contributions to the improvement of photocatalytic activity. However, Pd⁰ and PdO deposits on TiO₂ almost had no positive effect on NO oxidation. The mechanism of photocatalytic oxidation of NO in gas phase over Pd-modified TiO₂ was also proposed.