Is it permissible to dispose of the proceeds from usurious banks by donating them to help the mosque?

Usurious gains must be disposed of by spending them on general Muslim welfare, such as building schools and hospitals, or by giving them to the poor and needy. It is absolutely impermissible for the owner to benefit from them. Your spending of the usurious gains on the rent for the place you have taken as a mosque is a good deed.