A calibrated UV-LED based light source for water purification and characterisation of photocatalysis.

Photocatalysis has a potential to become a cost effective industrial process for water cleaning. One of the most studied photocatalysts is titanium dioxide which, as a wide band gap semiconductor, requires ultraviolet (UV) light for its photoactivation. This is at the wavelengths where the efficiency of present-day light emitting diodes (LEDs) decreases rapidly, which presents a challenge in the use of UV-LEDs for commercially viable photocatalysis. There is also a need for accurate photocatalysis measurement of remediation rates of water-borne contaminants for determining optimum exposure doses in industrial applications. In response to these challenges, this paper describes a UV-LED based photocatalytic test reactor that provides a calibrated adjustable light source and pre-defined test conditions to remove as many sources of uncertainty in photocatalytic analysis as possible and thereby improve data reliability. The test reactor provides a selectable intensity of up to 1.9 kW m-2 at the photocatalyst surface. The comparability of the results is achieved through the use of pre-calibration and control electronics that minimize the largest sources of uncertainty; most notably variations in the intensity and directionality of the UV light emission of LEDs and in LED device heating.

Angle dependent optical properties of polymer films with a biomimetic anti-reflecting surface replicated from cylindrical and tapered nanoporous alumina.

Anodic porous alumina nanostructures have been fabricated with tapered and cylindrical pores with a spacing of 100 and 200 nm and depth of 180-500 nm. The porous nanostructures were replicated into polymer films to create a moth-eye anti-reflecting surface by a roll-to-roll UV replication process. The angle dependent optical transmission of the resulting polymer films exhibited up to a 2% increase in transmission at a normal angle and up to a 5% increase in transmission at a 70° angle of incidence to an equivalent film with a surface replicated from polished aluminum. No significant difference was observed between the optical performance of moth-eye surfaces formed from cylindrical and tapered nano-pores.

Anodised titania nanotubes prepared in a glycerol/NaF electrolyte.

This paper discusses the preparation of titania nanotubes by anodisation of Ti in a glycerol-based electrolyte containing 0.5% wt of sodium fluoride (NaF). The influence of anodisation voltage and anodisation time on nanotube wall thickness, diameter and length has been investigated. The results indicate that nanotubes can be formed within a voltage range 10-40 V and that the tubular structure is lost when using a higher voltage. The diameter of the nanotubes is voltage dependent, with the widest tubes being obtained at the highest possible applied voltage of 40 V. An initial voltage ramp which increases at 100 mV/s to the anodisation voltage, rather than an instantaneous step, was observed to stabilise the metal-oxide interface. This enabled the growth of anodic films up to 5.5 microm in length by anodising for approximately 48 h. In the absence of a voltage ramp the films tended to collapse and become detached from the titanium electrode after 15-20 h. Electron microscopy observation suggests that the nanotubes in glycerol develop in a similar way to those produced in water-based media. The nanotubes formed using glycerol also exhibit ripples along the tube wall, although, growing at a slower rate, they are generally smoother than those formed in water.