The researchers created a composite material by attaching cellulose-derived carbon quantum dots, known as CQDs, to CdS nanoparticles. In laboratory tests, the optimized catalyst generated 7,812.5 micromoles of hydrogen per gram during five hours of visible-light irradiation. Under the same conditions, unmodified CdS produced 4,633.5 micromoles per gram. The results, published in Sustainable Carbon Materials, suggest that a renewable carbon material can help solve one of the central problems in solar photocatalysis: keeping light-generated electrical charges apart long enough to drive useful chemical reactions.

Hydrogen is often described as an energy carrier rather than a primary energy source. It can be produced using electricity or sunlight and later used in fuel cells, industrial processes, or energy-storage systems. When consumed in a fuel cell, hydrogen produces water rather than carbon dioxide at the point of use. Photocatalytic hydrogen production is especially attractive because it seeks to use sunlight directly to power the chemical conversion of protons into hydrogen gas. However, the efficiency and durability of photocatalytic materials remain significant obstacles to practical deployment.

CdS is a promising photocatalyst because its relatively narrow bandgap allows it to absorb a substantial portion of visible light. When CdS absorbs photons with sufficient energy, electrons are promoted from the valence band to the conduction band, leaving positively charged holes behind. The excited electrons can reduce protons to form hydrogen, while the holes participate in oxidation reactions. The difficulty is that electrons and holes can rapidly recombine, releasing their energy as heat or light before they reach the surface. CdS can also suffer from photocorrosion, a process that gradually damages the semiconductor during illumination.

To modify the material, the researchers produced CQDs from cellulose through a hydrothermal process. Cellulose, the structural polymer found in plant cell walls, can be converted under heat and pressure into nanoscale carbon particles with electronic and optical properties that differ from those of bulk carbon. Microscopy showed that the CQDs averaged approximately 3.5 nanometers in diameter and were distributed on the surface of CdS nanoparticles. The attachment process preserved the general structure of the CdS while creating an interface where charge transfer could occur.

The resulting composites absorbed visible light more effectively than pure CdS and displayed slightly narrower bandgaps. The best-performing formulation, designated 12CQDs/CdS, had a bandgap of approximately 2.01 electron volts, compared with 2.05 electron volts for unmodified CdS. Although the numerical shift appears small, changes in band structure and interfacial electronic states can influence how efficiently a photocatalyst uses incoming photons and how readily excited electrons move through the material.

The clearest evidence of improved charge management came from electrochemical measurements. The optimized CQDs/CdS composite reached an average photocurrent density of 49.9 microamperes per square centimeter, nearly 20 times higher than the 2.63 microamperes per square centimeter measured for pure CdS. A higher photocurrent indicates that more photogenerated charges are reaching the electrode and participating in external electrical processes rather than recombining inside the catalyst. The composite also showed lower charge-transfer resistance, suggesting that electrons could move more readily across the CQD–CdS interface.

The researchers propose that the carbon quantum dots perform two related functions. First, they act as photosensitizers, helping the material harvest visible light. Second, they serve as electron acceptors that capture excited electrons from CdS and help transport them away from locations where recombination is likely. By improving spatial separation between electrons and holes, the CQDs leave more electrons available to reduce protons into hydrogen. This interfacial process is central to the performance increase: the carbon dots do not simply add more surface area, but actively influence the movement and lifetime of charge carriers.

The study also reveals why adding more of the carbon material is not necessarily better. When the CQD loading becomes excessive, the particles can cover active sites on the CdS surface, block the arrival of light, or hinder the movement of reactants and products. The strongest performance therefore depended on carefully controlling the amount of CQDs rather than maximizing their concentration. Even at the optimized composition, however, hydrogen production declined during repeated photocatalytic cycles. This decrease indicates that photocorrosion of CdS remains unresolved and could limit the material’s long-term usefulness. Protective surface layers, cocatalysts, engineered heterostructures, and further tuning of CQD surface chemistry may help improve stability. By combining an abundant biomass-derived material with a visible-light semiconductor, the work offers a relatively simple route toward more efficient photocatalysts while reducing reliance on noble metals and elaborate architectures.

Subject of Research: Cellulose-derived carbon quantum dots combined with cadmium sulfide for visible-light photocatalytic hydrogen production.

Article Title: Cellulose carbon quantum dots decorated CdS nanocatalyst for enhanced visible-light photocatalytic hydrogen evolution

News Publication Date: 8-Jun-2026

Web References: Sustainable Carbon Materials: https://www.maxapress.com/scm; DOI: https://doi.org/10.48130/scm-0026-0020

References: Wang Z, Changotra R, Dong G, Yang J, He QS. 2026. Cellulose carbon quantum dots decorated CdS nanocatalyst for enhanced visible-light photocatalytic hydrogen evolution. Sustainable Carbon Materials 2: e025. DOI: 10.48130/scm-0026-0020

Image Credits: Zijing Wang, Rahil Changotra, Guofa Dong, Jie Yang, and Quan Sophia He

Keywords

Photocatalysis, hydrogen evolution, carbon quantum dots, cellulose, cadmium sulfide, visible-light catalysis, renewable energy, solar fuel, nanomaterials, photocorrosion

The research focused on methylene blue, a common synthetic dye prevalent in textiles, cosmetics, and medicine, as well as real wastewater from a potato processing plant. MAHC’s performance was evaluated in both batch adsorption tests and continuous fixed bed column setups, reflecting practical wastewater treatment scenarios. Notably, the fixed bed experiments revealed breakthrough times of 165 minutes for methylene blue solutions and 360 minutes for actual wastewater, underscoring its potential for real-world applications.

At the core of MAHC’s superior adsorption capacity — reaching a remarkable 1,635.28 mg per gram under optimal batch conditions — lies its engineered porous structure and active metal sites. Characterization showed a high specific surface area of 1,266.1 m²/g and a predominantly microporous architecture. The intricately designed iron and copper sites on the carbon matrix facilitate multiple pollutant interactions, including π–π bonding with dye molecules and pore-filling mechanisms.

Adsorption kinetics adhered to a pseudo second-order model, indicating adsorption occurred through chemisorption involving complex surface reactions rather than mere physical attachment. Furthermore, the observed Freundlich isotherm suggested multilayer adsorption on heterogeneous surfaces, which contrasts with simple monolayer adsorption typically seen in activated carbon adsorbents. Electrostatic forces played only a minor role in the uptake process, highlighting the significance of chemical interactions facilitated by the metal functionalities.

Corresponding authors Dr. Yulin Hu and Dr. Quan Sophia He remarked on the synergy between the metallic active sites and carbon framework, emphasizing this cooperation as a key driver for the material’s performance. This combinatory effect enables MAHC not only to trap contaminants physically but also to engage in chemical binding, presenting an advanced approach to pollutant removal from complex wastewater streams.

While these findings mark a significant stride towards sustainable water remediation, the team advises further research to benchmark MAHC against commercial activated carbons, explore other biomass precursors, and evaluate the material’s durability through repeated adsorption-desorption cycles. Additionally, since the optimal performance was observed at elevated temperatures around 44 °C, enhancing efficacy near ambient conditions remains a critical step for industrial feasibility.

This study exemplifies a promising circular economy strategy by valorizing wood waste and simultaneously addressing water pollution challenges. The integration of biomass recycling with wastewater treatment could pave the way for more eco-friendly and cost-effective purification technologies, potentially benefiting agriculture, public health, and environmental ecosystems.

Subject of Research: Experimental study on bimetallic activated hydrochar for wastewater treatment
Article Title: Adsorption of methylene blue dye and potato processing wastewater using bimetallic activated hydrochar: batch and fixed bed column experiments
News Publication Date: April 8, 2026
Web References: https://doi.org/10.48130/scm-0026-0014
References: Jalilian M, Nawazish B, Taborda R, He QS, Hu YL. 2026. Sustainable Carbon Materials 2: e019
Image Credits: Milad Jalilian, Bisma Nawazish, Regiane Taborda, Quan Sophia He, & Yulin Hu
Keywords: Adsorption, Activated Hydrochar, Bimetallic Adsorbent, Wastewater Treatment, Methylene Blue, Porous Carbon, Surface Science

The challenge of mitigating rising CO2 levels, which reached unprecedented concentrations of 422.5 parts per million in 2024, has intensified the search for efficient, robust carbon capture technologies. Conventional methods such as amine scrubbing have dominated industrial applications due to their ability to chemically bind CO2 from flue gases. However, these techniques entail significant drawbacks, including considerable energy expenditure, risk of chemical degradation, and substantial operational costs. These limitations have invigorated interest in solid adsorbent materials, particularly advanced carbons, which combine chemical resilience with cost-effectiveness.

Biochar, a highly porous carbonaceous residue produced by the thermochemical conversion of biomass waste, emerges as a compelling alternative. Its environmentally friendly lifecycle is carbon-negative, as it sequesters atmospheric carbon during production, simultaneously providing soil amendment benefits. Nevertheless, its application in CO2 capture has been hampered by intrinsic performance limitations related to suboptimal pore architectures and slow adsorption kinetics when compared to engineered activated carbons.

The research team devised a novel two-step activation approach combining phosphoric acid pre-treatment with potassium hydroxide (KOH) etching under microwave pyrolysis conditions. This method uniquely enables fine-tuning of the mesopore distribution, critical for optimizing the trade-off between adsorption capacity and transport kinetics. By carefully adjusting the phosphoric acid-to-biomass ratio, they engineered a biochar variant—referred to as PKBC-3—with an extraordinary specific surface area exceeding 3,000 square meters per gram, alongside a micropore volume surpassing one cubic centimeter per gram.

PKBC-3 demonstrated a record-high CO2 adsorption capacity of 3.434 millimoles per gram at standard room temperature and atmospheric pressure, positioning it at the forefront of biomass-derived adsorbents globally. This capacity is particularly noteworthy as it aligns with or surpasses values reported for conventional activated carbons, attesting to the exceptional efficacy of their synthetic strategy. Additionally, dynamic breakthrough analyses underscored the material’s rapid adsorption kinetics, especially when the mesopore fraction was precisely calibrated to approximately 40 percent.

This optimal mesopore proportion confers a hierarchical pore structure that facilitates swift diffusion of CO2 molecules into the micropore adsorption sites, thereby reconciling the inherent trade-off that historically constrained biochar performance. Traditionally, increasing micropores enhanced total adsorption capacity but slowed gas transport; conversely, a higher mesopore content accelerated kinetics but at the expense of capacity. The authors’ delineation of a mesopore threshold synthesizes these conflicting design criteria, offering a paradigm shift in biochar engineering.

By orchestrating targeted hierarchical porosity through their combined chemical activation and microwave pyrolysis protocol, the researchers maximized both adsorption capacity and operational velocity. This breakthrough underscores a significant leap toward industrial applicability, promising cost-effective carbon capture solutions compatible with flue gas treatment and broader climate mitigation strategies.

Complementing their achievement, the research team emphasized the sustainability and scalability of their method. Microwave-assisted pyrolysis drastically reduces energy consumption compared to conventional thermal treatments, and the use of abundant agricultural residues like corn straw ensures a renewable feedstock. Importantly, the chemical activation strategy employs relatively benign reagents with optimized usage, minimizing environmental impact during production.

The study’s success paves the way for subsequent investigations focused on functionalizing biochar surfaces to enhance selectivity against competing gases such as nitrogen and oxygen inherent in industrial exhausts. Such modifications could fine-tune adsorption affinity, further elevating material performance in diverse environmental contexts. The researchers also plan to scale up the process to pilot and industrial stages, aiming to demonstrate operational feasibility within existing CO2 capture infrastructure.

Supported by China’s National Natural Science Foundation and the Heilongjiang Provincial Key Research and Development Program, this research marks a critical milestone in sustainable carbon materials science. It exemplifies how strategic integration of chemical activation chemistry with advanced pyrolysis technologies can unlock novel adsorbent architectures, bridging laboratory innovation and real-world climate solutions.

As global policy frameworks increasingly prioritize carbon neutrality, the development of efficient and scalable CO2 capture materials like the PKBC-3 biochar becomes pivotal. Its combination of superior capacity, rapid kinetics, and sustainability can accelerate adoption in industries spanning power generation, manufacturing, and beyond. This advancement thus represents not just a scientific triumph but a crucial component in the global response to climate change challenges.

In sum, the team’s work redefines the potential of biochar materials, transforming them from mere soil amendments into high-performance adsorbents capable of competing with established carbon capture technologies. By balancing intricate pore structures with energy-efficient synthesis, this innovation charts a promising path toward mitigating one of the most pressing environmental issues of our time.

Subject of Research: Not applicable

Article Title: CO2 capture performances of H3PO4/KOH activated microwave pyrolyzed porous biochar

News Publication Date: 27-Oct-2025

Web References:
http://dx.doi.org/10.48130/scm-0025-0004

References:
Qiu T, Cao W, Xie K, Ahmad F, Zhao W, et al. 2025. CO2 capture performances of H3PO4/KOH activated microwave pyrolyzed porous biochar. Sustainable Carbon Materials 1: e004

Image Credits:
Tianhao Qiu, Weitao Cao, Kaihan Xie, Faizan Ahmad, Wenke Zhao, Ehab Mostafa & Yaning Zhang

Keywords:
Adsorption, Carbon dioxide, Porous materials, Pyrolysis