Humins, waste from biomass hydrolysis, are the main factor limiting the utilization efficiency of biomass carbon. In the present study, waste humins were employed for activated carbon production though KOH activation in a temperature range of 500–900 °C. The structure and properties of the activated carbons were studied, and a honeycomb-like macropore structure was observed. High activation temperature was demonstrated to be capable of promoting the formation of activated carbon with high surface area, high pore volume and high adsorption capacity. The activated carbon obtained by carbonization at 800 °C (KOH800) was selected as sorbent to adsorb methylene blue (MB) and phenol in aqueous solution, and the adsorption process can be explained by pseudo-second-order kinetic model. The adsorption behavior complies with Langmuir isotherm model and exhibits superior adsorption capacity of 1195 and 218 mg/g for MB and phenol, respectively. The impacts of surface area, acidic active sites and pore structures were also investigated, and it was found that the adsorption of approximately 44.0% MB and 39.7% phenol were contributed by the pores with apertures from 1.7 nm to 300 nm.

Four new donor–π–acceptor (D–π–A) structured organic sensitizers (CB1-4), with N-octyl or N-methoxyphenyl carbazole connected to a 2-cyanoacrylate BODIPY module through their 2 or 3-positions, were designed and synthesized for application in dye-sensitized solar cells (DSSCs). The photophysical and electrochemical properties were systematically studied and their performances as sensitizers in DSSCs were comparatively investigated. The structure–property relationship suggests that the electron-donating ability and substitution positions of the donor have a significant effect on these dyes' electronic and photovoltaic properties. Electron-rich N-methoxyphenyl carbazole as a donor and substitution at the 2-position shows a positive influence on the efficiency of DSSCs. Consequently, CB4, with the combination of these advantages, presents the broadest (300–650 nm) and strongest absorption profile with a high extinction coefficient (1.71 × 10⁵ M⁻¹ cm⁻¹) and the best photovoltaic performance with a short circuit photocurrent density of 10.20 mA cm⁻², an open circuit voltage of 600 mV, and a fill factor of 0.7, corresponding to a fairly good overall conversion efficiency of 4.28% under AM 1.5 irradiation (100 mW cm⁻²).