Table of contents

Aluminosilicate inorganic polymers have been proposed as low-energy cements since, unlike Portland cement, their production does not require high temperatures or generate large quantities of greenhouse gases. Other environmental protection applications for inorganic polymers are to encapsulate hazardous mining or radioactive wastes for safe long-term storage and as fireproof components for buildings and vehicles. However, newly developed methods for synthesising these materials have opened up the possibility of other novel environmental protection applications. These include porous cladding material for passive cooling of buildings, cost-effective exchange materials for removing heavy metals from wastewater, bacteriocidal materials for purifying polluted drinking water and materials for photodegrading hazardous organic environmental pollutants. The nature and synthesis of inorganic polymers for these environmental applications will be discussed here.

Synthesis of structured macroporous TiO₂ thin films on quartz substrate (macro-TiO₂/Q) was performed by a dip-coating method using poly(methyl methacrylate) (PMMA) microspheres as template. Obtained TiO₂ thin films kept high transparency and had anatase crystalline structure. SEM observations revealed that the macropores were uniformly formed on the film surface. The size of macropores was quite similar to the diameter of PMMA microspheres as template. In comparison to the nonporous TiO₂ thin films (TiO₂/Q), macro-TiO₂/Q exhibited twice higher photocatalytic activity for decolorization of methylene blue in water. Decomposition of acetaldehyde in gas phase also proceeded efficiently on macro-TiO₂/Q. Moreover, the surface of macro-TiO₂/Q was easily hydrophilized after a short period of UV light irradiation and maintained lower water contact angle in the dark for a long period as compared to those of TiO₂/Q.

CaAl₂O₄:(Eu,Nd)/TiO_2−xN_y composites were synthesized via two different methods, i.e., a two-step method (solvothermal reaction followed by mechanochemical treatment) and a one-step method (direct solvothermal dispersion method), and the photocatalytic activities were evaluated for deNO_x ability both under UV light (λ>290 nm) irradiation and after turning off the UV light. It was confirmed that TiO_2−xN_y nanoparticles with anatase phase could be uniformly dispersed on the surface of CaAl₂O₄:(Eu, Nd) by both method. However, the composites prepared by a one-step method possessed much larger specific surface areas, higher photocatalytic activity and more prolonged catalytic time after turning off the light than those by a two-step method, indicating that the solvothermal method is more appropriate for the synthesis of CaAl₂O₄:(Eu, Nd)/TiO_2−xN_y composite photocatalyst.

Anatase-phase TiO₂ films were prepared from amorphous TiO₂ films with using a novel crystallization technology in which 13.56 MHz rf (radio frequency) plasma is applied to the film samples for few minutes without heating. The obtained anatase TiO₂ films have almost the same photocatalytic degradation activity as that of the thermally-crystallized anatase TiO₂ films. Although the key parameter of this plasma crystallization process is the plasma gas pressure, the best plasma gas pressure depends on the plasma gas species and applied rf power and is independent to film materials nor substrate materials. Experimental results strongly suggest that the plasma crystallization is realized by the application of alternating rf electric field into the film materials. Easiness of plasma crystallization of TiO₂ films is found to depend on the film preparation conditions and this relation between crystallization easiness and preparation condition is different from the relation in the heat crystallization.

Yb-doped titanium dioxide (TiO₂) films deposited on glass substrate were prepared by radio-frequency (RF) magnetron sputtering. The effects of total sputtering pressure and Yb doping on the phase structure, surface morphology, surface roughness and optical properties of TiO₂ films were investigated. The results showed that all of Yb-doped TiO₂ films deposited under pure Ar and Ar/O₂ gas mixture at substrate heating temperature 500°C consisted of well crystalline anatase. It was demonstrated that the surface morphology and roughness of deposited films were strongly affected by the total sputtering pressure. The film sputtered under higher pressure (3Pa) has higher surface roughness with porous structure. Moreover, the increasing in surface roughness of deposited films when doping with Yb was observed. The absorption edge of transmittance of Yb-doped TiO₂ film was red-shifted compared to the pure TiO₂ film.

A natural mineral attapulgite was employed as a carrier of TiO_2−xN_y nanopaticles photocatalytst. The attapulgite/TiO_2−xN_y composites were prepared by soft grinding after hydrothermal synthesis of TiO_2−xN_y nanoparticles at 250°C for 10 min. The photocatalytic activities of the samples were evaluated for the oxidative destruction of NO. The composites showed excellent photocatalytic activity under both UV and visible light irradiation, where attapulgite/70 wt.% TiO_2−xN_y composites showed the best performance for NO destruction.

The phosphate supported Pt catalysts (Pt/AlPO₄, Pt/CePO₄, Pt/CeP₂O₇, Pt/SnP₂O₇, Pt/TiP₂O₇, Pt/Zn₃(PO₄)₂) were prepared by a conventional impregnation method to evaluate their selective catalytic reduction activity of NO_x under excess oxygen condition. Among them, good NO_x reduction activity was obtained on the Pt/AlPO₄ catalyst. Specific adsorption species during the NO_x reduction were checked by a diffuse reflectance infrared Fourier transform spectrum (DRIFTs) measurement to examine the reaction mechanism. Also NH₃ temperature programmed desorption measurements were performed for all catalysts and their catalytic properties were discussed from the viewpoints of solid acidity.