Photocatalytic valorization of lignin

A method for selective partial depolymerization of natural lignin source, the method comprising the steps of:

• (1) obtaining a natural lignin source;
• (2) performing a photocatalytic activation of a β-O-4 bond in the natural lignin source by using a photocatalytic activation system comprising a catalyst comprising tetrabutylammonium decatungstate (TBADT) and a light source with light in an ultraviolet region shined on the natural lignin source;
• and
• (3) adding an exogenous electron mediator/scavenger system comprising an exogenous electron mediator to promote a cleavage or a bond-scission of the β-O-4 bond and/or an exogenous electron scavenger to promote an oxidation of the β-O-4 bond;
• whereby the addition of the exogenous electron mediator increases a yield of an oligomer but decreases an amount of carbonyl (C═O) groups in the oligomer and the addition of the exogenous electron scavenger increases the amount of carbonyl (C═O) groups in the oligomer and slightly changes the yield of the oligomer, wherein the yield of the oligomer is a weight of the oligomer divided by a weight of the natural lignin source.