While 5G is being widely deployed around the world, the efforts from both academia and industry have started to propose and investigate various promising 6G techniques, among which Terahertz (THz) wireless ad hoc networks have drawn much research attention. With the recent development in nanomaterials, THz systems have been developed to support rapidly increasing demand for ultra-high data rates while addressing the spectrum scarcity and capacity limitation problems of current wireless communication systems. Towards this end, THz wireless techniques have been envisioned as one of the key technologies of 6G wireless networks, which boosts the range of applications of nanotechnology. However, due to the complexity in accurately characterizing THz-band wireless channels and interference models in the nanoscale scenarios, a number of technical challenges, such as capacity and mutual information modelling problems, need to be overcome for achieving such ultra-high-speed data rates in the THz band. To solve the above problems, we propose to maximize the mutual information in the THz band over wireless ad-hoc nano-networks. Particularly, we establish THz-band nano-communication system models. Then, we characterize the interference model and formulate and solve the mutual information maximization problem for our proposed THz-band nano-communication schemes. Simulation results are included, which validate and evaluate our proposed schemes in the THz band.