Metal oxide tends to absorb moisture, S-OH (S is surface).

So it is ok, it can be used to sense any gases.

In term of photocatalysis, it also can be used, maybe only need higher energy to excite the electron to conduction band.

Firstly, you must know what is the initial resistivity (or conductivity) without any gas. There may be a change (probably) a small change, in case the gas is reacting with the sensing film. If there is not change then it means that sensing gas is not interacting with sensing coating.

Try to have a semiconducting film, and not an insulating film.

or try some other sensing coatings, which can provide a change in resistivity.

Any material has own conductivity or if you want its reverse value namely resistivity but of different magnitudes. It depends. As Artur Braun said it's empirical. If you have semiconducting metal oxide and suitable equipment able to measure its conductivity/resistance, you can register even its small change in response to a gas in accord with K. Sreenivas recommendation.

Dear Poshan,

your commonplace case, with a "zero" DC conductivity is a characteristic example for the demanding of an alternative to

1)the DC conductivity measurement, e.g. implementing

2)an AC conductivity[1] or even better, an EIS[2] measurement.

Another, unique, but trivial, example, comparable to your significant case, is the "zero DC" conductivity of an ideal Capacitor, at a near real ("ideal"), DC, "zero Frequency", mode.

1. If I could propose a Freq. band of F ~1kHz, to ~10kHz.

2. If an an EIS apparatus is available, at home, or nearby you.

Gas sensing applications or photocatalysis depends one and/or of the following;

1- changes of structural properties

2- Changes of the optical rpoperties

3- Changes of the electrical properties

items 2 and 3 always depend on item No.1

The most important thing that you mentioned that "

no conductivity and has more resistivity"

Please see the attached file, it is impossible to have no conductivity and more resistivity. resistivity should be had infinity values "not more values"

otherwise insulators.

Any how to check sensing properties, different concentrations of a certain gas should be applied to your focused material and check at least one of the mentioned three properties.

I wish this is useful and help you.

Yours

A. El-Denglawey