IUPAC definition:

"Region of the electromagnetic spectrum extending from about 400 nm to 760 nm. This is the wavelength region to which the human eye is sensitive. There are no precise limits for the spectral range of visible radiation since they depend upon the amount of radiant power reaching the retina and on the responsivity of the observe"

TiO2 does not absorb light at >400 nm. You need to provide more information to answer your question. 

There is no sense to do the measurements unless you have modified material that absorbs visible light.

You can observe photocurrents for TiO2 in the range 300-380 nm. For the details of the measurement please check one of my publications.

Article Photocatalytic Activity of TiO2 Modified with Hexafluorometa...

Article On Oxygen Activation at Rutile- and Anatase-TiO2

The photochemical reaction proceeding on a TiO2 surface when irradiated with UV light (400 nm)  by several approaches  which including TiO2 modification :

1- metal-ion implanted TiO2 (using transition metals): Cu, Co, Ni, Cr, Mn, Mo, Nb, V, Fe, Ru, Au, Ag, Pt

2- non-metal doped-TiO2 :N, S, C, B, P, I, F

3- doping metal ions into the TiO2 lattice

4- dye photosensitization on the TiO2 surface

Hello all,

Thank you for your answers. I actually forgot to mention that it is Nitrogen doped TiO2 that's why I wanted to measure the photocurrent.

Regards

Comparative study on UV and visible light sensitive bare and doped titanium dioxide photocatalysts for the decomposition of environmental pollutants in water

Article in Applied Catalysis A General 417-418:26-36 · December 2011

DOI: 10.1016/j.apcata.2011.12.018

Peroxo group enhanced nanorutile as visible light active photocatalyst

Article in Catalysis Today · November 2016

DOI: 10.1016/j.cattod.2016.11.012

Thank you very much

Regards