that for the hard wall, the solute density profile, and hence the steady-state chucker location, depends on the position of the absorbing box boundary, since a linear concentration gradient of solute arises between the colloid and the box boundary. However, the qualitative features of our results are independent of the boundary position. In this work, we have used computer simulations to study the physics of an active colloid (a “chucker”) of radius R$_{1}$ , which produces solute particles of radius R$_{2}$ isotropically on its surface, at a rate k$_{c}$ . Most of our simulations have used a Monte Carlo scheme in which the chucker is modelled as a hard sphere and the solute particles as Asakura-Oosawa ( i.e. mutually non-interacting) spheres. Our MC simulations were complemented by an overdamped Langevin dynamics approach in which the chucker is represented as a point particle which experiences a force proportional to the gradient of a concentration field of solute, this field being computed analytically using the Green’s function for free diffusion. The Langevin dynamics approach has the advantage that we can tune the prefactor that links the osmotic force to the solute concentration gradient: this provides a crude way to model hydrodynamic effects close to the chucker surface. Our MC simulations of an isolated chucker in free space show diffusive behaviour, from which we extract an effective diffusion constant D$_{eff}$ . This varies nonmonotonically with the chucking rate. For small values of k$_{c}$ , solute chucking enhances diffusion. We interpret this as being due to the chucker being “pushed along” by a self-generated solute concentration gradient; the same behaviour is recovered in our Langevin dynamics simulations. An increase in D$_{eff}$ as a function of k$_{c}$ was recently predicted analytically by Golestanian [11]. In our MC simulations, when the chucking rate becomes large, the chucker tends to become caged by newly generated solute particles, hampering its diffusion. The result is therefore a peak in D$_{eff}$ at intermediate chucking rate. In our simulations, the solute particles do not interact. For more realistic, interacting solutes, we might expect crowding to kick in at lower chucking rates, shifting the peak in D$_{eff}$ towards smaller k$_{c}$ . A quantitative comparison between our MC simulation results and Golestanian’s theoret- ical prediction reveals that the simulations are in agreement with theory for a hydrodynamic length λ $_{= (}$√$_{2}$$_{/}$$_{3)}$$_{R}$$_{1}$$_{, for large values of the ratio between the sizes of the chucker and of the}$ 16 IV. DISCUSSION