One-dimensional TiO2 (1D TiO2) nanomaterials with unique structural and functional properties have been extensively used in various fields including photocatalytic degradation of pollutants, photocatalytic CO2 reduction into energy fuels, water splitting, solar cells, supercapacitors and lithium-ion batteries. In the past few decades, 1D TiO2 nanostructured materials with a well-controlled size and morphology have been designed and synthesized. Compared to 0D and 2D nanostructures, more attention has been paid to 1D TiO2 nanostructures due to their high aspect ratio, large specific surface area, and excellent electronic or ionic charge transport properties. In this review, we present the crystal structure of TiO2 and the latest development on the fabrication of 1D TiO2 nanostructured materials. Besides, we will look into some critical engineering strategies that give rise to the excellent properties of 1D TiO2 nanostructures such as improved enlargement of the surface area, light absorption and efficient separation of electrons/holes that benefit their potential applications. Moreover, their corresponding environmental and energy applications are described and discussed. With the fast development of the current economy and technology, more and more effort will be put into endowing TiO2-based materials with advanced functionalities and other promising applications.

A review of one-dimensional TiO2 nanostructured materials for environmental and energy applications

On the reverse indentation size effect and microhardness measurement of solids

The microhardness indentation load/size effect (ISE) on the Knoop microhardness of single crystals of TiO2 and SnO2 has been investigated. Experimental results have been analysed using the classical power law approach and from an effective indentation test load viewpoint. The Hays/Kendall concept of a critical applied test load for the initiation of plastic deformation was considered, but rejected to explain the ISE. A proportional specimen resistance (PSR) model has been proposed that consists of the elastic resistance of the test specimen and frictional effects at the indentor facet/specimen interface during microindentation. The microhardness test load, P, and the resulting indentation size, d, have been found to follow the relationship 
$$P = a_1 d + a_2 d^2 = a_1 d + (P_c /d_0^2 ) d^2$$

 The ISE is a consequence of the indentation-size proportional resistance of the test specimen as described by a
1. a
2 is found to be related to the load-independent indentation hardness. It consists of the critical indentation load, P
c, and the characteristic indentation size, d
o.

The microhardness indentation load/size effect in rutile and cassiterite single crystals

Differential Thermal Analysis

The role of friction between the microhardness indenter and the test specimen is addressed through the analysis of dry (unlubricated) and lubricated tests on iron by Atkinson and Shi. Quantitative evaluation through a proportional specimen resistance model accurately describes the results. It suggests that friction is a major portion of the observed hardness increase at low test loads, the indentation size effect. The ISE is related to the surface-area-to-volume ratio of the indentation, which is inversely related to the indentation dimension.

The frictional component of the indentation size effect in low load microhardness testing

Investigations on indentation induced hardness and fracture mechanism in flux grown DyAlO3 crystals

Gadolinium tartrate crystals in the form of spheru!itoe were synthesized by using a controlled diffusion system in sillica gel. Characterization of the material was performed by utilizing the techniques of chemical analysis, X-ray and electron diffraction, infrared and mass spectroscopy, and by As thermal behaviour. The material turns out to be a dihvdrate and the chemical composition vvoethus established as Gd2(C4H4O6)3 · 2H2O. The data obtained from the thermal analysis show the tendency of the material to decompose, and this is further confirmed by mass spectroscopy The decomposition process is completed in four steps until gadolinium oxide is obtained at 840* C. The energetics of the reactions at each stage of decomposition have been examined and mechanisms for the decomposition reactions are proposed.

Characterization and thermal behaviour of gel-grown gadolinium tartrate crystals

Dielectric characteristics of mixed Gd-Ba molybdate crystals grown at ambient temperatures by the gel encapsulation technique

Spherulitic growth of gadolinium tartrate dihydrate crystals by controlled diffusion in silica gel is reported. The influence of growth parameters e.g., reactant concentration, gel pH and gel ageing, on the size, quality and nucleation density of the spherulites has been studied. It is observed that under varying experimental conditions involving change in reactant concentrations, gel pH and gel ageing, the material crystallizes in the form of spherulites. The results of growth kinetics are discussed. Scanning electron microscopy confirms spherulites to be aggregates of single crystallites, with each micro-sized crystal exhibiting a cuboid morphology. Surface structures exhibited by the micro-sized crystals indicate their growth by two-dimensional nucleation mechanism.

Growth and Kinetic Studies of Spherulitic Gadolinium Tartrate Crystals from Silica Gel

Sherulites, crystal aggregates and platelets of Di2 (C4H4O6)3 · 5H2O mixed crystals were grown in gel using the single tube diffusion method. The material was characterized by using different techniques such as chemical analysis, EDAX, X-ray and electron diffraction, infrared and mass spectroscopy. The thermal behaviour of the material was studied using differential thermal analysis, DTG, thermogravimetric analysis and differential scanning calorimetry. The material is thermally unstable and starts decomposing at 50‡ C. Thermal analysis results indicate the application of the contracting cylindrical kinetic model for the solid state reactions involved in the decomposition process. The values of kinetic parameters, e.g. order of reaction, activation energy and frequency factor are worked out. The implications are discussed.

P. N. Kotru

Papers

Investigations on indentation induced hardness and fracture mechanism in flux grown DyAlO3 crystals

Characterization and thermal behaviour of gel-grown gadolinium tartrate crystals

Dielectric characteristics of mixed Gd-Ba molybdate crystals grown at ambient temperatures by the gel encapsulation technique

Growth and Kinetic Studies of Spherulitic Gadolinium Tartrate Crystals from Silica Gel

Characterization and thermal behaviour of gel grown mixed rare-earth (Didymium) tartrate crystals