  We investigate the variation of the charged anti-de Sitter black hole under
charged particle absorption by considering thermodynamic volume. The variation
exactly corresponds to that expected as the first law of thermodynamics.
Nevertheless, we find the decrease of the Bekenstein-Hawking entropy for
extremal and near-extremal black holes under the absorption to be an
irreversible process. This violation of the second law of thermodynamics is
only found in the case considering thermodynamic volume. We test the weak
cosmic censorship conjecture affected by the violation. Fortunately, the
conjecture is still valid. However, extremal and near-extremal black holes do
not change their configurations under the absorption. This is quite different
from the case without thermodynamic volume.
