TiO2 nanoparticles for water treatment

The management of contaminants of emerging concern (CECs) in water bodies is particularly challenging due to the difficulty in detection and their recalcitrant degradation by conventional means. In this review, CECs are characterized to give insights into the potential degradation performance of similar compounds. A two-pronged approach was then proposed for the overall management of CECs. Light-driven oxidation processes, namely photo/Fenton, photocatalysis, photolysis, UV/Ozone were discussed. Advances to overcome current limitations in these light-driven processes were proposed, focusing on recent trends and innovations. Light-based detection methodology was also discussed for the management of CECs. Lastly, a cost–benefit analysis on various light-based processes was conducted to access the suitability for CECs degradation. It was found that the UV/Ozone process might not be suitable due to the complication with pH adjustments and limited light wavelength. It was found that EEO values were in this sequence: UV only > UV/combination > photocatalyst > UV/O3 > UV/Fenton > solar/Fenton. The solar/Fenton process has the least computed EEO < 5 kWh m−3 and great potential for further development. Newer innovations such as solar/catalyst can also be explored with potentially lower EEO values.

Udara bersih merupakan kebutuhan mendasar bagi makhluk hidup. Pada lingkup yang lebih kecil seperti rumah, kebutuhan udara bersih sangatlah vital. Hal ini karena kualitas udara dalam ruang sangat mempengaruhi kesehatan manusia dimana hampir 90% hidup manusia berada dalam ruangan. Kualitas udara dalam ruang dapat dipengaruhi oleh beberapa faktor diantaranya adalah sistem ventilasi ruangan. Saat ini ventilasi merupakan salah satu tempat sistem aliran udara baik dari luar maupun kedalam ruangan. Namun, umumnya udara dari luar rungan banyak mengandung berbagai polutan pencemar yang berbahaya bagi penghuni rumah. Zat pencemar dari luar ruangan diantaranya karbon monooksida (CO), sulfur oksida (SO), nitrogen oksida (NO), hidrokarbon (H2C), dan partikulat (debu) yang berasal dari pabrik semen, industri metalurgi, konstruksi, dan kendaraan bermotor; jenis mikroorganisme seperti bakteri, virus dan jamur yang dapat menyebarkan berbagai penyakit pada manusia. Berdasarkan hal ini diperlukan usaha untuk meminimalisir konsentrasi polutan udara yang masuk ke dalam ruangan melalui pemanfaatan Air Cleaning System (ACe) menggunakan nano-TiO2 terdoping yang dikombinasikan dengan karbon aktif yang dipasang pada sistem ventilasi sebagai filter udara. TiO2 merupakan katalis semikonduktor yang paling efektif karena tidak beracun, harganya terjangkau, melimpah di alam, bersifat inert, pengoksidator kuat, dapat bekerja pada suhu ruangan dan stabilitas yang tinggi terhadap fotokorosi. Pemanfaatan semikonduktor TiO2 telah banyak digunakan dalam bidang aplikasi pembersihan, degradasi polutan dan mikroorganisme di udara diantaranya self-cleaning dan antifogging dengan prekursor TiO2, self-cleaning cat akrilik, self-cleaning senyawa ammonium (NH4+), penurunan kadar gas polutan di udara seperti HC dan SO2, CO2, NO2, deaktivasi mikroorganisme patogen seperti bakteri E. coli, S. aureus dan E. faecalis dan jenis jamur seperti C. albicans dan A. niger. Penggunaan fotokatalis TiO2 kurang maksimal jika digunakan dalam keadaan murni karena mempunyai luas permukaan yang relatif rendah sehingga daya adsorpsinya lemah dan juga memiliki energi celah pita yang besar (3,25 ev) yang mengakibatkan hanya efektif pada daerah Uvsihingga fotokatalis TiO2 perlu disintesis dalam ukuran nano,
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didoping dan dikombinasikan dengan suatu material adsorben seperti karbon aktif sehingga dapat bekerja maksimal dibawah sinar tampak. Mekanisme penurunan kadar polutan udara menggunakan ACe pada filter ventilasi yakni ketika nano-TiO2 terdoping yang dikombinasikan dengan karbon aktif diaktivasi menggunakan sinar (hv) pada panjang gelombang tertentu akan menghasilkan elektron spesis kimia (e-) dan hole (h+). Hole (h+) akan berinteraksi dengan uap air (H2O) di udara menghasilkan OH radikal (•OH) yang bersifat sebagai oksidator kuat. Elektron (e-) akan bereaksi dengan O2 di udara membentuk radikal superoksida (•O2-) yang bersifat sebagai reduktor. Spesis radikal kimia yang dihasilkan bersama-sama akan digunakan untuk mendegradasi polutan udara yang akan masuk ke dalam ruangan melalui sistem filter ventilasi. Pemanfaatan Air Cleaning System (ACe) menggunakan nano-TiO2 terdoping yang dikombinasikan dengan karbon aktif yang dipasang pada sistem ventilasi akan dapat menurunkan kadar polutan udara sehingga udara menjadi bersih dan lebih sehat bagi penghuni bangunan atau rumah.

A novel class of photocatalytic coating capable of degrading bacterial and chemical contaminants in the
presence of visible sunlight wavelengths was produced by depositing a stable photocatalytic TiO2 film on
the internal lumen of glass bottles via a sol–gel method. This coating was prepared in either undoped form
or doped with nitrogen and/or copper to produce visible light-active TiO2 films which were annealed at
600 ◦C and were characterized by Raman and X-ray photoelectron spectroscopy. The presence of doped
and undoped TiO2 films was found to accelerate the degradation of methylene blue in the presence
of natural sunlight, while copper-doped TiO2 films were found to accelerate bacterial inactivation (of
Escherichia coli and Enterococcus faecalis) in the presence of natural sunlight.

This paper reports a simple, biogenic and green approach to obtain narrow band gap and visible light-active TiO 2 nanoparticles. Commercial white TiO 2 (w-TiO 2) was treated in the cathode chamber of a Microbial Fuel Cell (MFC), which produced modified light gray TiO 2 (g-TiO 2) nanoparticles. The DRS, PL, XRD, EPR, HR-TEM, and XPS were performed to understand the band gap decline of g-TiO 2. The optical study revealed a significant decrease in the band gap of the g-TiO 2 (E g = 2.80 eV) compared to the w-TiO 2 (E g = 3.10 eV). The XPS revealed variations in the surface states, composition, Ti 4+ to Ti 3+ ratio, and oxygen vacancies in the g-TiO 2. The Ti 3+ and oxygen vacancy-induced enhanced visible light photocatalytic activity of g-TiO 2 was confirmed by degrading different model dyes. The enhanced photoelectrochemical response under visible light irradiation further supported the improved performance of the g-TiO 2 owing to a decrease in the electron transfer resistance and an increase in charge transfer rate. During the TiO 2 treatment process, electricity generation in MFC was also observed, which was ~0.3979 V corresponding to a power density of 70.39 mW/m 2. This study confirms narrow band gap TiO 2 can be easily obtained and used effectively as photocatalysts and photoelectrode material.

Surfaces which possess extraordinary water attraction or repellency depend on surface energy, surface chemistry, and nano-and microscale surface roughness. Synergistic superhydrophilic-underwater superoleophobic surfaces were fabricated by spray deposition of nanostructured TiO 2 on stainless steel mesh substrates. The coated meshes were then used to study gravity driven oil−water separation, where only the water from the oil−water mixture is allowed to permeate through the mesh. Oil−water separation efficiencies of up to 99% could be achieved through the coated mesh of pore sizes 50 and 100 μm, compared to no separation at all, that was observed in the case of uncoated meshes of the same material and pore sizes. An adsorbed water on the TiO 2 coated surface, formation of a water-film between the wires that form the mesh and the underwater superoleophobicity of the structured surface are the key factors that contribute to the enhanced efficiency observed in oil−water separation. The nature of the oil−water separation process using this coated mesh (in which the mesh allows water to pass through the porous structure but resists wetting by the oil phase) minimizes the fouling of mesh so that the need for frequent replacement of the separating medium is reduced. The fabrication approach presented here can be applied for coating large surface areas and to develop a large-scale oil−water separation facility for oilfield applications and petroleum industries.

Visible light active PtOx@M-TiO2 and PtOx@P-TiO2 (x=0, 1 and 2) nanocomposites were fabricated via a simple, green and environmentally benign process using an electrochemically active biofilm. The formation of the PtOx@M-TiO2 and PtOx@P-TiO2 nanocomposites was confirmed by X-ray diffraction, ultraviolet–visible–near infrared spectrophotometry, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS revealed the presence of Pt0, Pt2+ (PtO) and Pt4+ (PtO2) species on the surface of M-TiO2 and P-TiO2. The presence of mixed valence states of PtOx on the surface of the PtOx@M-TiO2 nanocomposite and defect states in M-TiO2 helps absorb visible light more efficiently compared to the PtOx@P-TiO2 nanocomposite. Cyclic voltammetry, electrochemical impedance spectroscopy and linear scan voltammetry confirmed the enhanced photoelectrochemical performance of the PtOx@M-TiO2 nanocomposite compared to the PtOx@P-TiO2 nanocomposite under visible light irradiation. Furthermore, the PtOx@M-TiO2 nanocomposite was used as a cathode material in microbial fuel cells and showed a higher power density compared to the PtOx@P-TiO2 nanocomposite and plain carbon paper due to the high catalytic activity of platinum and defective M-TiO2.

Heterogeneous photocatalysis offer many possibilities for finding appropiate environmentally friendly solutions for many of the the problems affecting our society (i.e., energy issues). Researchers are still looking for novel routes to prepare solid photocatalysts able to transform solar into chemical energy more efficiently. In many developing countries, biomass is a major energy source, but currently such countries lack of the
technology to sustainably obtain chemicals and/or fuels from it. The Roadmap for Biomass Technologies, authored by 26 leading experts from academia, industry, and government
agencies, has predicted a gradual shift back to a carbohydrate-based economy. Biomass and biofuels appear to hold the key to satisfy the basic needs of our societies for the sustainable production of liquid fuels and high value-added chemicals without compromising the scenario of future generations. In this review, we aim to discuss various design routes for nanostructured photocatalytic solid materials in view of their applications in the selective transformation of lignocellulosic biomass to high value-added chemicals.

The present work mainly aimed to synthesize different weight percentages (0.25-1.00 wt%) of Manganese (Mn 2+) and Magnesium (Mg 2+) bimetal ions doped TiO 2 nanomaterial assisted with different weight percentages (5-15 wt%) of Gemini surfactant (GS) using sol-gel method. The bimetal doped and undoped TiO 2 photocatalysts were characterized by X-ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, Fourier Transform Infrared Spectroscopy (FT-IR), UV-Visible Diffused Reflectance Spectroscopy, Transmission Electron Microscopy, Brunauer-Emmett-Teller surface area analyzer, and Photoluminescence Spectroscopy. Characterization results revealed that mesoporous multi-particle anatase TiO 2 nanoparticles with a narrowed band gap, small particle size, and high surface area were formed due to the combined effect of Mn 2+ /Mg 2+ bimetal ions doping and effective encapsulation of GS over the initially formed TiO 2 nanoparticles. The surface elemental composition of the 0.25 wt% Mn 2+ and 1.00 wt% Mg 2+ bimetal doped TiO 2 in the presence of 10 wt% of GS (after calcination) revealed the presence of both the metal dopants Mn 2+ and Mg 2+ along with the Ti and O and their chemical interactions were further confirmed by FT-IR results. The photocatalytic activity of these catalysts was assessed by the degradation of Methyl Red using visible light irradiation. To understand the effect of different reaction parameters on the photocatalytic activity of the nanocatalysts such as the dopant concentration, surfactant concentration, catalyst dosage, solution pH, and initial dye concentration were investigated and optimized to achieve the best performance. The photoluminescence results conclude that OH radicals are the crucial reactive species responsible for oxidative photocatalytic degradation of Methyl Red.

The study is aimed at evaluating the potential of immobilized TiO 2-based zeolite composite for solar-driven photocatalytic water treatment. In that purpose, TiO 2-iron-exchanged zeolite (FeZ) composite was prepared using commercial Aeroxide TiO 2 P25 and iron-exchanged zeolite of ZSM5 type, FeZ. The activity of TiO 2-FeZ, immobilized on glass support, was evaluated under solar irradiation for removal of diclofenac (DCF) in water. TiO 2-FeZ immobilized in a form of thin film was characterized for its morphology, structure, and composition using scanning electron microscopy/energy-dispersive x-ray spectroscopy (SEM/EDX). Diffuse reflec-tance spectroscopy (DRS) was used to determine potential changes in band gaps of prepared TiO 2-FeZ in comparison to pure TiO 2. The influence of pH, concentration of hydrogen peroxide, FeZ wt% within the composite, and photocatalyst dosage on DCF removal and conversion efficiency by solar/ TiO 2-FeZ/H 2 O 2 process was investigated. TiO 2-FeZ demonstrated higher photocatalytic activity than pure TiO 2 under solar irradiation in acidic conditions and presence of H 2 O 2 .

Visible light-active TiO 2 (m-TiO 2) nanoparticles were obtained by an electron beam treatment of commercial TiO 2 (p-TiO 2) nanoparticles. The m-TiO 2 nanoparticles exhibited a distinct red-shift in the UV-visible absorption spectrum and a much narrower band gap (2.85 eV) due to defects as confirmed by diffuse reflectance spectroscopy (DRS), photoluminescence (PL), X-ray diffraction, Raman spectroscopy, electron paramagnetic resonance, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS) and linear scan voltammetry (LSV). The XPS revealed changes in the surface states, composition, Ti 4+ to Ti 3+ ratio, and oxygen deficiencies in the m-TiO 2. The valence band XPS, DRS and PL results were carefully examined to understand the band gap reduction of m-TiO 2. The visible light-responsive enhanced photocatalytic activity of m-TiO 2 was demonstrated by degrading methylene blue and brilliant blue G. The EIS and LSV in the dark and under visible light irradiation further support the visible light-induced photocatalytic activities of the m-TiO 2 due to a decrease in electron transfer resistance and an increase in photocurrent. This study confirms that m-TiO 2 can be used effectively as a photocatalyst and photoelectrode material owing to its enhanced visible light-induced photocatalytic activity.

"En este artículo se presenta el efecto de las sales inorgánicas MgSO4, NaCl y CaCO3 en la desinfección fotocatalítica del agua. Se usó TiO2-P25 como fotocatalizador y E. Coli como microorganismo contaminante. Las pruebas de desinfección se realizaron mediante la iluminación controlada de reactores batch cargados con agua contaminada, sales y TiO2. Los resultados de estas pruebas fueron usados para determinar los parámetros cinéticos de un modelo tipo Langmuir-Hinshelwood. Se encontró que las sales tienen una fuerte influencia sobre la inactivación fotocatalítica de E. Coli, y que cada sal y su concentración afectan la desinfección de forma diferente y en el siguiente orden: NaCl>CaCO3>>MgSO4. Adicionalmente, el valor de los parámetros calculados fue diferente para cada sal, evidenciando que las sales afectan el proceso por varios mecanismos relacionados con las interacciones ion-bacteria, ion-especie oxidante e ion-TiO2."

In the present research work a potentially improved Copper (Cu) and Boron (B) codoped TiO 2 nano materials were synthesized by varying the different dopant concentrations (Copper 0.25, 0.50, 0.75, 1 wt% and Boron 0.25, 0.50, 0.75, 1 wt%) using solgel method for the photocatalytic degradation of Lissamine Green B. In order to investigate the physical, chemical and optical properties of a catalyst, which play a key role in its photocatalytic activity, as prepared samples were characterized by various instrumental techniques. The crystalline phase study performed for all the samples using X-ray powder diffraction (XRD) confirmed the formation of anatase TiO 2. Chemical composition of the prepared catalyst investigated by X-ray photo electron spectroscopy (XPS) affirmed the presence of constituent elements (Ti, O, Cu & B) on the catalyst surface. The surface microstructure studied by field emission scanning electron microscopy (FE-SEM) revealed that the TiO 2 particles having spherical shape with rough surface morphology. The average particle size and surface area of the catalyst determined by high-resolution transmission electron microscopy (HRTEM) and Brunauer-Emmett-Teller (BET) surface area analyser, revealed that the codoped catalyst shows a high percentage of small particles of size 6.8 nm and a high surface area of 135.6 m 2 /g, respectively. The band edge absorption shift of the samples was determined by diffuse reflectance spectroscopy analysis (DRS) and the results exhibited that among all the codoped samples Copper 0.25 wt% and Boron 1 wt% (CBT1) catalyst shows a reduced band gap energy of 2.73 eV. The characterization results supported the photocatalytic activity of the catalyst for the degradation of Lissamine Green B within 90 min at the optimum reaction parameters such as dopant concentration of Cu at 0.