Q:

Is Talaq effective when given without any witness, just between husband in the absence of wife?

A:

You should seek divorce through the legal channels rather than merely using verbal pronouncement of divorce.

On the proper method of divorce, please consult the answer linked below:

What Are the Procedure and Rulings of Divorce?

https://aboutislam.net/counseling/ask-the-scholar/family/procedure-rulings-divorce/

Allah Almighty knows best.