In this paper we propose a novel adaptive scheme for full duplex communication of secondary users (SUs) in a cognitive radio network. The secondary network operates in three modes; Cooperative Sensing (CS), Full Duplex Transmit and Sensing (FDTS), and Full Duplex Transmit and Receive (FDTR). In the CS mode, the secondary nodes detect the activity of primary users (PUs) through a novel cooperative MAC protocol and will decide the systems mode of operation in the subsequent spectrum hole. In the FDTS mode one of the SUs senses the PUs activity continuously whilst transmitting to another node. In the FDTR mode, the SUs would communicate bidirectionally in an asynchronous full duplex (FD) manner, with decreased maximum and average collision durations. Analytical closed forms for probability of collision, average collision duration and cumulative collision duration, as well as throughput of the SU network are derived, and performance of the proposed protocol in terms of above-mentioned metrics, its effectiveness, and advantages over conventional methods of sensing and transmission are verified via simulations