Photo-electro-chemical decomposition of water is done to?

Photo-electro-chemical splitting of water uses solar energy at an electrode to break water into hydrogen and oxygen, producing clean hydrogen fuel.

Removing pathogens is a job for disinfection methods such as chlorination or ultraviolet treatment, not this process.

Removing dissolved metals is done by techniques like precipitation, ion exchange or adsorption, which are unrelated to water splitting.

Removing oil and grease relies on skimming, flotation or gravity separators, again a different operation.

Here light generates charge carriers in a semiconductor that then drive the water splitting reaction.

The hydrogen so produced is valued as a storable, carbon free energy carrier.