Abstract Sustaining crop yield is a growing challenge due to soil fertility loss and climate change. As a result, fertiliser application is increasing to sustain yield and counteract low fertiliser use efficiency. Developing nutrient-efficient fertilisers, for example by combining biochar with fertilisers, is thus crucially needed. In this context, the development of biochar-mineral complex (BMC) fertilisers into liquefied products suitable for broadacre application is highly innovative. This study aimed to explore the agronomic benefits and economic viability of four novel liquefied BMCs designed for application within a pasture cropping system. The different forms of developed BMCs included two non-enriched BMCs (BMC1 and BMC2) that were micronised using different techniques, a phosphorus (P)-enriched BMC (BMC3), and a nitrogen (N)-enriched BMC (BMC4), all applied both with- and without co-fertilisation. Soil biochemistry, plant NP uptake, NP balances, plant yield and cost–benefit were examined. Pasture yield was significantly higher using BMC1 and BMC3 with co-fertilisation than without, most likely due to improved P availability, as evidenced by positive P balances. Yield was significantly enhanced under BMC4 at 42.20 t ha −1 , compared with BMC1 at 21.90 t ha −1 , BMC2 at 19.41 t ha −1 , BMC3 at 25.81 t ha −1 , the fertilised control at 18.75 t ha −1 and non-fertilised control at 11.53 t ha −1 . Only BMC4 showed positive NP balances, suggesting that pasture did not absorb N and P from the existing soil reserve. Soil microbial composition and abundance were not affected by the applied BMC treatments in short term. The benefit–cost ratio ranged from 1.94 to 2.54, indicating economic viability of the BMC products and suggesting a great potential of biochar-based fertilisers for wide adoption to other crops. Graphic abstract

Abstract Based on the concept of resource utilization, this study successfully prepared a green and highly efficient nitrogen-doped biochar catalyst (N-BC-800) using agricultural waste cotton hulls as a raw material. This catalyst was then applied to the ozone-catalyzed degradation of N,N-diethyl-meta-toluamide (DEET), a typical insect repellent in water bodies. The apparent second-order rate constant reached 2358 M −1 s −1 , representing a 106-fold increase compared to the O 3 system alone, and a 25-fold increase compared to the O 3 /BC system. Experimental characterization and theoretical analysis indicate that C=O groups and pyridinic N structures on the material surface serve as primary catalytic active sites. These synergistically promote ozone decomposition and generate highly reactive intermediates which are further converted into reactive oxygen species (ROS), significantly enhancing DEET degradation performance. This catalyst exhibits excellent stability and applicability in real aquatic environments. It demonstrates broad-spectrum degradation effects on multiple pollutants while significantly reducing the ecotoxicity of reaction byproducts. This study provides theoretical support and practical pathways for developing highly efficient, green ozone-catalyzed materials. Graphical Abstract

Abstract Biomass materials offer the advantages of low cost, abundant availability, and renewability, making them sustainable and environmentally friendly alternatives to petroleum-based thermal insulation materials. Spent coffee ground (SCG), a type of biomass generated after brewing coffee, has been used as a filler for thermal insulation composites. However, developing SCG-based composites with superior thermal insulation performance remains a significant challenge due to the low porosity of SCG. Herein, a highly porous SCG biochar (SB) was fabricated by a simple carbonization process optimized for temperature and atmosphere. SB-based thermal insulation polymer composites were designed and fabricated for the first time, employing the SB as the filler and biodegradable ethyl cellulose (EC) as the matrix. Meanwhile, the SB was pre-mixed with environmentally friendly solvents (water, ethanol, and propylene glycol) selected based on the chemical interaction within the material system to prevent the impregnation of SB pores with the EC. The chemical and morphological properties of the SB were discussed in terms of their influence on the thermal insulation properties of the fabricated composite. The thermal conductivity and heat transfer mechanism of the SB-based composites were systematically verified using steady-state heat transfer theory. The biodegradable SB-based composite demonstrated outstanding thermal insulation property (0.04 W m −1 K −1 ) comparable to commercial expanded polystyrene. More importantly, the thermal insulation composites developed in this work consisted of environmentally friendly and sustainable materials, free from hazardous or toxic substances. These thermally insulating and biodegradable SB-based polymer composites are expected to be widely utilized in various thermal insulation applications.

Abstract Tea ( Camellia sinensis ) cultivation, central to global agriculture and livelihoods, is increasingly challenged by soil degradation, heavy metal contamination, and climate stressors largely driven by intensive practices. Because tea agroecosystems typically occupy acidic, nutrient-poor soils, sustainable management is essential. Biochar, a carbon (C)-rich product of biomass pyrolysis, has emerged as a promising amendment to restore soil health, mitigate contaminants, and strengthen crop resilience. This review synthesizes recent advances on the biochar–soil–tea nexus across five dimensions: (i) soil physicochemical and structural properties, (ii) microbial diversity and functions, (iii) nutrient mobilization and efficiency, (iv) tea productivity and quality, and (v) heavy-metal detoxification. Evidence from field and controlled studies shows that biochar can buffer soil acidity, enhance nutrient retention, restructure microbial communities, reduce pollutant bioavailability, and improve tea growth and quality. In addition, it offers a practice guide for tailoring biochar application based on feedstock and pyrolysis conditions to achieve specific soil and plant health goals. Furthermore, biochar contributes to C sequestration and greenhouse gas mitigation, situating its use within the broader framework of climate-smart agriculture. Despite these benefits, outcomes are highly context-dependent, shaped by feedstock type, pyrolysis conditions, soil characteristics, and application rate. Critical research gaps remain, including scarce tropical field studies, limited long-term field evaluations, inconsistent biochar characterization, and insufficient understanding of cultivar-specific and microbial interactions. By mapping these uncertainties and outlining research priorities, this review provides a foundation for optimizing biochar use in tea systems and guiding region-specific strategies for sustainable cultivation in a changing climate.

Abstract In the context of carbon neutrality targets, biochar is widely promoted as a soil amendment to sequester organic carbon in soils. Although a wealth of research has illustrated the benefits of biochar to plants, its potential toxicity to soil fauna and microbes requires serious consideration. The aim of this study was to perform a meta-analysis of experimental data on biochar effects (i.e. percentage change in endpoints after biochar application compared to the control group) on plants, animals, and microorganisms. The experimental data were extracted from 61 papers and consists of 1329 data points. In a next step, machine learning was used to develop a classifier to predict, whether biochar has positive or negative consequences on soil organisms based on biochar and soil properties. The meta-analysis shows that the effect of biochar is negatively correlated with the biochar application rate, biochar pH, pyrolysis temperature, and soil pH. A random forest classifier was then developed to classify whether biochar was “beneficial” or “hazardous” based on four types of descriptors: biochar properties, soil properties, test organism, and endpoint type. The accuracy of the best model achieved an R 2 of 0.79. In the next step, a quantitative model was developed to predict the effect with an R 2 of 0.48. The model is of great significance for understanding the role of biochar in soil and improving the quality control strategy for biochar production. Graphical Abstract

Abstract The low fertilizer utilization efficiency and metal(loid) contamination have become dual challenges that constrain the production of rice and thus food security. To address these issues, a life-cycle greenhouse study was conducted with rice ( Oryza sativa ) grown in soil co-contaminated with cadmium (Cd) and arsenic (As) and treated with several synthetic fertilizers. These fertilizers included regular fertilizers (F), biochar-based fertilizers (BF) and nano-biochar-based fertilizers (NBF), each formulated with varying nitrogen:phosphorus:potassium (N:P:K) ratios (I, II, and III). The results revealed a differential suppression of Cd (strongest under F-I, followed by NBF-III) and As (strongest under F-II, followed by NBF-I) in rice grains, attributable to disparities in their environmental chemistry, bioavailability, and plant-mediated uptake and translocation mechanisms. While BF enhanced catalase and alkaline phosphatase activities, NBF more effectively stimulated urease activity throughout the 0–10 cm layer and sucrase activity in the deeper 5–10 cm zone. Notably, NBF increased soil metabolic diversity under Cd and As stress while strengthening the genetic regulatory capacity and environmental adaptability of microbial communities. Furthermore, NBF dynamically regulated the migration of Cd and As into porewater, resulting in more stable and effective immobilization compared to BF and F treatments. These findings highlight that the application of biochar, particularly nano-biochar, for paddy soil remediation necessitates a contaminant-specific and nutrient-managed strategy. Tailoring both the biochar type and the accompanying N:P:K ratio is crucial for targeting the biogeochemical behavior of the dominant contaminant, thereby ensuring grain safety and supporting sustainable rice production. Graphic Abstract

Abstract Engineered biochar with enhanced photochemical properties holds great potential for environmental remediation. However, natural humic substances, crucial players in environmental redox processes, are structurally complex and slow-forming, hindering mechanistic insights and practical applications. Here, we propose a co-engineering strategy that combines biochar with artificial humic substances synthesized from pine sawdust via controlled hydrothermal humification (180–340 °C). Modulating the hydrothermal temperature can yield artificial humic substances with diverse degradation degrees of lignin, yielding tailored phenolic architectures and electron-donating capacities (EDC). Using Ag⁺ photoreduction as a model reaction, we demonstrate that artificial humic substances produced at 340 °C exhibit optimal phenol content and the strongest reducing capacity (19.2-fold greater than that of substances synthesized at 180 °C). Notably, higher molecular weight fractions (> 5 kDa) of artificial humic substances were found to dominate Ag⁺ photoreduction due to their enriched phenolic content and superior EDC. Mechanistic investigations reveal that photo-excited phenolic groups generate superoxide radical (O 2 •− ), initiating Ag⁺ reduction via a ligand-to-metal charge transfer (LMCT) pathway. Moreover, we discovered a previously overlooked phenomenon: hydrochar undergoes photo-induced dissolution, further enhancing photoreduction. This work provides new insights into the temperature-dependent lignin transformation into redox-active artificial humic substances and highlights the dynamic photochemical behavior of engineered biochar (hydrochar) under solar irradiation. Graphical Abstract

Abstract This study presents the development of a novel, disposable, and eco-friendly electrochemical device based on biochar-modified screen-printed electrodes (SPE/BC) for the detection of the antibiotic trimethoprim. Biochar, derived from sewage sludge, was applied as a nanomaterial to enhance the sensitivity of the sensor for trimethoprim quantification in environmental, biological, and pharmaceutical samples. Characterization techniques, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy, were used to assess the properties of biochar. Surface area, pore volume, and pore diameter were measured using the Brunauer–Emmett–Teller method. The electrochemical sensor performance was analyzed using impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry, revealing a strong synergistic effect on the trimethoprim oxidation process. The device showed high sensitivity with a detection limit of 71.0 nmol L⁻ 1 over a linear range of 1.75–231.43 μmol L⁻ 1 . Recovery studies in synthetic urine, tap water, and pharmaceutical tablets demonstrated recoveries of 92%–99%, with no sample pretreatment. The sensor exhibited selectivity towards common interferents such as sulfamethoxazole, urea, and ascorbic acid, making it a practical tool for detecting trimethoprim as an emerging pollutant. Graphical Abstract

Living wall systems (LWSs) help to alleviate the climate and biodiversity harms associated with buildings and bring benefits to building occupants. Their performance can be variable and existing research points to the planting substrate as a key design factor. This study provides quantitative evidence on the physical, thermal and moisture performance of three planting substrates that vary according to the proportion of biochar added to green waste compost (GWC). Thermal conductivity (Wm−1 K−1), thermal resistivity (mK W−1), volumetric moisture content (%) and mass (g) are measured for each fraction, replicated six times. Controlled drying procedures were employed, measuring these properties at a range of moisture levels. Data analysis finds that volumetric moisture content and biochar fraction have a statistically significant (p ≤ 0.05) effect on thermal conductivity. Added biochar is associated with non-linear reductions in thermal conductivity at low moisture levels. This suggests increasing the biochar fraction while reducing moisture in the substrate of a LWS will reduce its thermal conductivity, with a 100 mm planting substrate with 30% biochar and 30%vol moisture content providing 0.82 m2 KW−1 of thermal resistance, compared to 0.46 m2 KW−1 without added biochar. The methods build on previous work to assess the properties of different planting substrates for LWSs, providing a practical, lab-based assessment of biochar. The data produced are useful for researchers and professionals seeking to understand how biochar additions impact irrigation and thermal performance when specifying and designing LWSs and underline the potential value of biochar for improving the thermal performance of green infrastructure more widely.Graphical

Not all biochar is equal. We clarify the frequent conflation between biochar carbon stability and soil co-benefits across research, policy, and markets. While stability ensures long-term carbon storage, co-benefits rely on more surface functionality from less stable biochar. Decoupling these dimensions enables designing biochar optimized for distinct functions.