Internet of Nano-Things (IoNT) is an expansion of the Internet of Things (IoT) with the capacity to monitor extremely fine-grained events with sensors on a scale ranging from one to a hundred nanometers. One major challenge for this type of communication paradigm is to determine the identity of the transmitting nodes and the events. From previous works, we know that different amount of energy is discharged in the environment from different events. This motivates us to propose an energy-neutral event recognition framework using pulse position modulation in which the event information is transmitted by the sensors that use the energy harvested from the event. In this framework, we use pulse position to identify transmitting nodes communicating with a single receiver. However, using this approach, we can also encode the identity of multiple receivers when a single node communicates with them without employing an addressing scheme in IoNT networks. In both cases, the energy observation of the received pulse helps in identifying the event type. The feasibility of the proposed framework is demonstrated by a large number of numerical simulations which include terahertz channels. We find that the proposed framework achieves 99% accuracy for detecting ten different event types at a distance of 30 mm.