<p>Photopyroelectric techniques were used to characterize fluids and evaluate the adsorption efficiency of mesoporous silica nanoparticles (MSNs) for methyl green. Optical absorption coefficients at 660&#xa0;nm were measured for MSNs exposed to various concentrations of methyl green solutions. Measurements of this optical property were obtained under three different conditions: dye solutions at different concentrations with and without MSNs; the supernatants of the dye solutions with MSNs (after 30&#xa0;min of adsorption followed by centrifugation); and the MSN pellet formed after centrifugation, redispersed in water. This approach enabled the determination of the adsorption efficiency of MSNs for methyl green. The methodology can be extended to evaluate the adsorption efficiency of nanoparticles with other pigments by adjusting the measurement wavelength or by accounting for additional factors, such as nanoparticle shape and size.</p> Graphical abstract <p></p>