Photoreactive titanate nanomaterials for water purification systems

University of Technology, Sydney. Faculty of Engineering and Information Technology.Increasing water scarcity and environmental considerations are calling for more effective means to purify industrial and urban wastewaters. Advanced oxidation processes are able to effectively remove many persistent and toxic pollutants from water to enable the use and reuse of impaired quality raw water sources. Among these processes, heterogeneous photocatalysis has some notable inherent advantages, such as relative process simplicity, and the minimal generation of waste streams. Unfortunately, the commercially available photocatalysts show poor efficiency in the utilisation of natural solar radiation and are difficult to separate and recover from treated water, which results in high operational costs. In order to alleviate these recognised problems, this thesis explored an improved method of material synthesis to produce nanomaterials with desirable properties. The investigation of peroxide method at high pH values showed that this facile approach offers great potential for the fabrication of various nanoparticles, nanostructures, and thin films deposits. The shape, size, structure and surface properties of the resulting photocatalysts were simply controlled through the process pH, the time of reaction, and the chemical composition of the solvent base. Both partial and complete dissolution of the precursors was accomplished to fabricate various, crystalline and amorphous anatase and alkali titanate end products. The use of ammonium hydroxide base was more advantageous, since it provided a very simple means to achieve simultaneous N doping. Effective N-doping of Degussa P25 commercial photocatalyst was simply achieved using highly concentrated (25%) ammonium hydroxide base in 24 h time at room temperature in an open reactor. The raw product slurries were neutralised with acid, washed with water, and aged until dry at 75 °C. Additional doping (co-doping) with Ag was achieved by adding AgNO3 to the raw slurries. The resulting nanoparticles had elongated rod and needle-like shapes, 2-3 times larger specific surface area (92.9-144.6 m2g-1) than the precursor P25, and 5.4-6.5 nm mesopore sizes. These photocatalysts were remarkably effective in the photobleaching of Methylene Blue under visible light, and simulated solar light illuminations. Therefore, this method is suitable to improve the performance of currently available commercial photocatalysts. Na-titanate microspheres with 700-800 nm diameter were produced at low (25-80 ◦C) temperatures using NaOH for base, and P25 precursor in the peroxide method. Both the raw and calcined products showed very high adsorption affinity towards Methylene Blue dye, and were also capable of its degradation under UV light without minimal loss of performance after five complete treatment cycles. The calcined product showed higher catalytic activity, and could be fully recovered from the spent slurry by gravity settling. Exchanging Na with H in titanates microspheres in HCl solution resulted in the formation of hydrogen-titanate nanofibres, which were transformed into anatase nanofibres after annealing at 550 °C for 6 h. The nanofibres had average specific surface area of 31.5 m2/g, average pore volume of 0.10 cm3/g and average pore size of 50 Å. These products also were effective adsorbent of the model pollutant and adsorbents and good photocatalyst under simulated solar light illumination. No reduction in photocatalytic activity was observed over three complete treatment cycles, and the effective separation of nanofibres was achieved by gravity settling resulting in low residual solution turbidity. Such nanofibres may also be used to produce paper-like photoreactive filter materials. An easily separable fibrous photocatalyst was produced by depositing H-titanate nanofibres on wool fibres serving as bio-template. The calcined end-product showed anatase crystal phase and nanofibrous morphology (about 50 μm length and 9.5 μm diameter), having about 24 m2/g specific surface area with mesoporous characteristics. These nanofibres were effective in the photocatalytic degradation of humic acid model pollutant solution under UV light irradiation. The performance of this photocatalyst showed only a small decrease after three complete treatment cycles, and the microfibres were easily separated from the treated solution by sedimentation with very low supernatant turbidity

Characterisation of titanium tetrachloride and titanium sulfate flocculation in wastewater treatment

Flocculation with titanium tetrachloride (TiCl4) and titanium sulfate (Ti(SO4)2) was investigated in terms of different coagulant doses, pH, turbidity, dissolved organic carbon (DOC), UV-254, colour, zeta potential, particle size and molecular weight distribution. The two coagulants were compared with the commonly used coagulants such as ferric chloride (FeCl3) and aluminium sulfate (Al2(SO 4)3). Titanium tetrachloride showed the highest turbidity removal, while titanium sulfate showed the highest reduction of UV-254 and colour at all pH values. The four coagulants were found to have similar organic removal up to 60-67% and resulted in similar organic removal in terms of various MW ranges. The decantability of the settled flocs was very high for titanium tetrachloride, titanium sulfate and ferric chloride compared with aluminium sulfate. The dominating coagulation mechanisms for titanium tetrachloride and titanium sulfate are still to be studied, since different precipitation reactions might take place at different pH even without flocculant addition. Titanium tetrachloride and titanium sulfate were found as effective new coagulants in wastewater treatment not only in terms of organic matter removal, but also in sludge reduction through the production of titanium dioxide. © IWA Publishing 2009

Synthesis and characterisation of potassium polytitanate for photocatalytic degradation of crystal violet

© 2014 . Potassium titanate nanostructures were synthesised by hydrothermal treatment of TiO2 (P25) in KOH and H2O2. As-produced powders were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption methods. Longitudinally-oriented-wire-like structures with a length up to several micrometres and diameters ranging from 10 to 30nm were obtained. Larger size fibrous nanowires resulting from the hydrothermal treatment showed high affinity in adsorbing crystal violet (CV), which was mainly due to their high surface area. The photocatalytic bleaching of CV solution revealed that the wires are photoactive under ultraviolet light irradiation. Macroporous nanowires are considered as effective adsorbents of CV, capable of photocatalytic degradation, and they can be easily separated from the solution by settling

Blended fertilizers as draw solutions for fertilizer-drawn forward osmosis desalination

In fertilizer-drawn forward osmosis (FDFO) desalination, the final nutrient concentration (nitrogen, phosphorus, potassium (NPK)) in the product water is essential for direct fertigation and to avoid over fertilization. Our study with 11 selected fertilizers indicate that blending of two or more single fertilizers as draw solution (DS) can achieve significantly lower nutrient concentration in the FDFO product water rather than using single fertilizer alone. For example, blending KCl and NH 4H 2PO 4 as DS can result in 0.61/1.35/1.70 g/L of N/P/K, which is comparatively lower than using them individually as DS. The nutrient composition and concentration in the final FDFO product water can also be adjusted by selecting low nutrient fertilizers containing complementary nutrients and in different ratios to produce prescription mixtures. However, blending fertilizers generally resulted in slightly reduced bulk osmotic pressure and water flux in comparison to the sum of the osmotic pressures and water fluxes of the two individual DSs as used alone. The performance ratio or PR (ratio of actual water flux to theoretical water flux) of blended fertilizer DS was observed to be between the PR of the two fertilizer solutions tested individually. In some cases, such as urea, blending also resulted in significant reduction in N nutrient loss by reverse diffusion in presence of other fertilizer species. © 2012 American Chemical Society

Hydrogen production affected by Pt concentration on TiO <inf>2</inf> produced from the incineration of dye wastewater flocculated sludge using titanium tetrachloride

TiO 2 from the incineration of dye wastewater flocculated sludge using TiCl 4 coagulant was produced. Optimal catalyst amount and Pt-loading on TiO 2 were studied for the production of H 2 by photocatalytic reforming of methanol (6% vol.). On the other hand, BTSE (biologically treated sewage effluent) was flocculated using TiCl4 and produced sludge was incinerated to generate TiO 2 . TiO 2 was loaded with optimum Pt and added to the supernatant in a photocatalytic reactor to test the efficiency of using remaining organics as a “sacrificial reagent” for photocatalytic hydrogen production. Dissolved organic carbon (DOC) and molecular weight distribution (MWD) were measured for nanofiltration (NF) and TiCl 4 flocculation followed by photocatalysis. TiO 2 (from the incineration of BTSE flocculated sludge using TiCl4) was produced and loaded with 0.5% Pt. Results showed that the optimum concentration of TiO 2 (from dye wastewater) for H 2 production was 0.3 g/L, while the optimum amount of Pt was 0.5%. DOC and MWD removal was similar for the flocculation of BTSE followed by photocatalytic reaction and the NF process. Remaining organic compounds after flocculation could not be used as sacrificial reagent to induce H 2 production. Further investigations on studying the UV intensity and/or identifying organic/inorganic scavengers to inhibit H 2 production are underway. © 2010, Taylor & Francis Group, LLC

Fertilizer drawn forward osmosis process for sustainable water reuse to grow hydroponic lettuce using commercial nutrient solution

© 2017 Elsevier B.V. This study investigated the sustainable reuse of wastewater using fertilizer drawn forward osmosis (FDFO) process through osmotic dilution of commercial nutrient solution for hydroponics, a widely used technique for growing plants without soil. Results from the bench-scale experiments showed that the commercial hydroponic nutrient solution (i.e. solution containing water and essential nutrients) exhibited similar performance (i.e., water flux and reverse salt flux) to other inorganic draw solutions when treating synthetic wastewater. The use of hydroponic solution is highly advantageous since it provides all the required macro- (i.e., N, P and K) and micronutrients (i.e., Ca, Mg, S, Mn, B, Zn and Mo) in a single balanced solution and can therefore be used directly after dilution without the need to add any elements. After long-term operation (i.e. up to 75% water recovery), different physical cleaning methods were tested and results showed that hydraulic flushing can effectively restore up to 75% of the initial water flux while osmotic backwashing was able to restore the initial water flux by more than 95%; illustrating the low-fouling potential of the FDFO process. Pilot-scale studies demonstrated that the FDFO process is able to produce the required nutrient concentration and final water quality (i.e., pH and conductivity) suitable for hydroponic applications. Coupling FDFO with pressure assisted osmosis (PAO) in the later stages could help in saving operational costs (i.e., energy and membrane replacement costs). Finally, the test application of nutrient solution produced by the pilot FDFO process to hydroponic lettuce showed similar growth pattern as the control without any signs of nutrient deficiency

Synthesis, characterisation and separation of photoreactive Hydrogen-titanate nanofibrous channel

Australia is the world's largest wool producing country, accounting for about 25-30% of world production. As a biotemplate, we explored the possibility of using wool to produce micro-channel of Hydrogen-titanate nanofibres through morphology transcription of wool microfibres. Hydrothermal method was adopted to synthesise titanate nanofibres. A facile method of impregnation followed by incineration at 600 °C was utilised to prepare the nanofibrous channel. Anatase undoped nanofibrous (average nanofibre diameter = 44 nm) channel of around 50 μm in length and an average diameter of 9.5 μm were obtained. The photocatalytic activity of nanofibrous channel was monitored under UV irradiation for the decomposition of humic acid in aqueous solution using an aerobic batch reactor system. The photodegradation results showed that UV 254 absorbing moeities and DOC were respectively reduced by 82% and 66% after 3 h of photoreaction at 1 g/L catalyst load. The novel nanofibrous channel could be easily separated from the aqueous suspension by sedimentation after the end of the photocatalytic reaction. © 2010 Elsevier B.V

Water reclamation by heterogeneous photocatalysis over titanium dioxide

© 2016 American Society of Civil Engineers. This chapter presents the fundamentals and basic principles of water reclamation by heterogeneous photocatalysis (HP). The effects of important operational parameters on the overall treatment efficiency of photocatalytic system are addressed in the chapter in terms of photocatalyst loading, pollutant concentration, pH and temperature of water, dissolved oxygen, and light intensity. The most popular semiconductor used in HP is Titanium dioxide (TiO2) for being relatively inexpensive, chemically stable, and nontoxic. Most water remediation technologies generate a significant amount of wastewater that requires costly retreatment or discharge to evaporation ponds, rivers, and oceans. HP processes that decompose aqueous contaminants are highly dependent on the reaction conditions and the setup of photocatalytic reactors. Visible-light responsive photocatalysts promise a more effective utilization of solar energy. Doping and co-doping of titania is a practical approach toward obtaining improved visible-light active photocatalysts