Hydrochar from Pine Needles as a Green Alternative for Catalytic Electrodes in Energy Applications.

Hydrothermal carbonization (HTC) serves as a sustainable method to transform pine needle waste into nitrogen-doped (N-doped) hydrochars. The primary focus is on evaluating these hydrochars as catalytic electrodes for the oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR), which are pivotal processes with significant environmental implications. Hydrochars were synthesized by varying the parameters such as nitrogen loading, temperature, and residence time. These materials were then thoroughly characterized using diverse analytical techniques, including elemental analysis, density measurements, BET surface area analysis, and spectroscopies like Raman, FTIR, and XPS, along with optical and scanning electron microscopies. The subsequent electrochemical assessment involved preparing electrocatalytic inks by combining hydrochars with an anion exchange ionomer (AEI) to leverage their synergistic effects. To the best of our knowledge, there are no previous reports on catalytic electrodes that simultaneously incorporate both a hydrochar and AEI. Evaluation metrics such as current densities, onset and half-wave potentials, and Koutecky-Levich and Tafel plots provided insights into their electrocatalytic performances. Notably, hydrochars synthesized at 230 °C exhibited an onset potential of 0.92 V vs. RHE, marking the highest reported value for a hydrochar. They also facilitated the exchange of four electrons at 0.26 V vs. RHE in the ORR. Additionally, the CO2RR yielded valuable C2 products like acetaldehyde and acetate. These findings highlight the remarkable electrocatalytic activity of the optimized hydrochars, which could be attributed, at least in part, to their optimal porosity.

Efficient synthesis and investigation of waste-derived adsorbent for water purification. Exploring the impact of surface functionalization on methylene blue dye removal.

In pursuit of sustainable water management, the preparation of adsorbent materials via waste upcycling for water purification practices plays a decisive role. The sulphonated biochar, PiNe-SO3H, employed to target the methylene blue dye adsorption, was successfully synthesized via a mild, step-economical chemical carbonization-functionalization reaction. The presence of SO3H groups on the PiNe-SO3H surface played a critical role in significantly enhancing the adsorption capacity. The observed MB dye uptake was predominantly attributed to chemisorption processes as evidenced by the results from kinetics, thermodynamics, and isotherms. To further confirm the role of -SO3H in the adsorption mechanism, a comparison was made with other PiNe materials lacking sulphonic groups, highlighting the superior adsorption capacity of PiNe-SO3H. Additionally, a fast and efficient regeneration process was proposed to develop a truly waste minimized protocol, enabling the recovery of up to 94 % of the ethanolic mixture used during this step.