The speciation and transport of metals in the environment is controlled by numerous factors, including water chemistry and the presence of colloidal and particulate matter. For example, it is well-known that metals bind to the surfaces of clays, bacteria, humic acids, and iron oxides, directly impacting their mobility in groundwater and surface water. Often ignored is the presence of particulate black carbon (PBC), which makes up on average 15% of the particulate organic matter (POC) content in global rivers. PBC originates from biochar produced by fires, where biomass is pyrolyzed at elevated temperatures and in oxygen-limited conditions, often leading to graphene-like carbon with low surface functional group densities. However, recent research has shown that PBC is photooxidized quickly in rivers and may, therefore, act as a significant sorbent for metals in river systems. This leads to two questions: (1) when forests and forest fires emerged in the Devonian, approximately 400 million years ago, how did pyrolytic carbon influence the transport of metals in groundwater and surface water to estuaries and deltas, and ultimately the marine rock record, and (2) given renewed interest in applying biochar at large scales as a soil amendment to improve crop growth and sequester potentially toxic metals, what will be the impacts of this application on water quality and metals transport? In this talk, I will provide an overview of our knowledge of biochar surface reactivity, its use in water and soil remediation, and potential implications of colloidal biochar now and in the geologic past.

Remediation of aqueous systems from pollution is a decades-old problem, with activated carbon and biochars produced from biogenic waste feedstocks having emerged as a sustainable, low-cost and environmentally friendly option. Similarly manganese oxides (MnOx) are some of nature’s most ubiquitous metal scavengers and play an essential role in the oceanic and soil redox cycles. Manganese oxide and biochar composites (MnOx-BC) are a class of materials attracting attention from within the remediation community and beyond. Produced sustainably from biowaste feedstocks, porous carbon composites can be tuned by selection of precursor feedstocks as well the physicochemical parameters of the thermochemical synthesis conditions. Manganese(IV) oxide - Biochar nano-composites (MnOx-BC) integrate the large surface area and redox capabilities of Mn(IV)-oxides with the high sorption capacity and surface functionality of different biochars. These multi-scale carbon-based composites have all the essential properties – tunable porosity, surface functionality and redox activity – for the capture of a wide array of inorganic pollutants such as mercury and other heavy metals. Mn(IV) oxides additionally possess oxidative capabilities aiding the photodegradation of complex organic pollutants such as dyes, or the reduction and subsequent complexation of Hg(0) to Hg(II). To understand the complex reaction network and dynamic interplay between redox transformations and complexation mechanisms, this study presents a range of MnOx-BCs with differing Mn oxidation states and biochar feedstocks (oak wood, rice husk, spent coffee grounds) to allow for targeted synthesis of a superior MnOx-BC material for mercury capture. Using X-ray absorption spectroscopy and scanning electron microscopy, we have revealed the significant impact of biochar surface functionality and bulk chemistry on the Mn phase resulting from three MnOx impregnation protocols.

Less than one percent of the earth’s water is easily accessible to us as fresh water and nearly half of this water is heavily polluted with microplastics, pesticides, and antibiotics due to waste from human establishments and agriculture. This research aimed to remove these key classes of contaminants by manipulating biochar surface area, controlling the chemical composition and catalytic properties for oxidative breakdown, adding surface complexing agents, and modifying intrinsic pore size. Six different kinds of engineered biochar were placed in water with 100µM initial pp-DDT, pp-DDE, dimetridazole, and bisphenol-A concentrations. Results show that catalyst and surface complexing agent presence coupled with high surface area are key for contaminant removal: manganese oxide and thiol functionalized milled rice husk biochar removed over 98% pp-DDT, 94% pp-DDE, 53% dimetridazole, and 95% bisphenol A were removed within 10 minutes. General trends in data demonstrate that high surface area, catalyst presence, increased pore size, thiol doping, and high carbon composition are key for contaminant sequestration. These results have the potential to revolutionize the water filtration industry by providing globally available, sustainable, and affordable means of purifying water. Integrating engineering with environmental chemistry, a filter capitalizing on biochar properties can be created for worldwide distribution at a cost of less than $1 per month and a filtration rate exceeding that of commercial filters for use in domestic, urban, industrial, agricultural, and aquatic settings.

Anaerobic digestion (AD) is used extensively for the sustainable management of a wide variety of waste. The main product of AD is biogas, an alternative gaseous biofuel, composed principally of methane. The operation of anaerobic digesters is often affected by inhibitory compounds present in the organic feedstocks or produced during their hydrolysis. These can be detrimental, reducing biogas yields and in some cases leading to system failure.  Among the reported approaches for mitigating such problems include the addition of adsorbent materials during digestion. Carbonaceous materials - such as activated carbons, biochar from pyrolysis and hydrochars from hydrothermal carbonisation of biomass - have been proposed as suitable options due to their potential for mitigation of the inhibitory NH₄⁺, improving the methane metabolism, reducing lag time, and facilitating the syntrophic metabolism between the different microorganisms involved in AD. Even though there are indications of their positive effect on the stability of the AD process and improved quality of digester, their full potential as adsorbent materials in AD has not been properly assessed. This study has investigated the impact of biochar and hydrochar on anaerobic digestion at laboratory scale biochemical methane potential (BMP) tests and performed a principal component analysis to compare with the literature review. Large differences were observed between the addition of biochar and hydrochar in this study. Hydrochar leads to lower methane production and higher accumulation of organic acids. The addition of BC leads to higher methane production with lower temperature biochars being favoured. The effect of the chars is related to their different chemical and physical properties, particularly acid/alkaline nature, surface functionality and surface area. Extensive analysis of the chars has been performed by XPS has allowed potential mechanisms to be proposed. The benefits of biochar augmentation and its influence on different feedstocks are discussed. 

Porous biochar is the thermochemical decomposition products of crop wastes and biologically derived materials. It garners increasing interest across ever-expanding domains due to its cheap and sustainable origins, ease of production, extensive porosity and large surface area as well as abundant surface functionality. Since biochar is also non-toxic and therefore compatible with environmental systems, it is of great interest in soil or water contaminant degradation and immobilisation. This is in contrast to more traditional inorganic ion-exchange technology, which becomes easily fouled in groundwater and may leach further toxic components.Biochar can also be activated to enhance contaminant uptake and retention, or even incorporated into composites, with other bio-compatible materials, in order to improve their stability and industrial value.While numerous studies show favourable contaminant uptake to activated biochar, data which elucidate binding mechanisms is largely lacking, in part due to the varied and amorphous nature of biochar. Further, the effect of full effect of activation upon its pore architecture is not fully understood. If activated biochar is to truly rival ion-exchange technology, it is crucial to unravel the mechanisms which underpin its function. This will inform the next generation of biochar-based remediation technology and allow for further enhancements.X-ray spectroscopic techniques are unparalleled in providing both atomic-scale mechanistic/chemical data and internal morphological data which shed light on the physicochemical processes underpinning contaminant immobilisation. Here we present X-ray absorption spectroscopy (EXAFS) data on strontium binding to a biochar hydrogel composite as well as X-ray Computed Tomography (XCT) data showing the effect of activation on the pore space volume, tortuosity, and pore size distribution.

There is current interest in producing value-added biorenewable materials and chemicals from biomass in order to provide sustainable alternatives to petroleum-derived products. One area of investigation in this field is the development of sustainable carbons. These materials represent low cost, scalable, economically attractive renewable carbon materials. These may be specifically engineered for a wide range of applications such as energy storage, catalysis and environmental sorbents [1–3]. Currently there are two principal processes for producing these materials: pyrolysis and hydrothermal carbonisation (HTC). Pyrolysis is the thermal treatment of biomass in the absence of oxygen at temperatures between 400 – 800 °C and produces pyrolysis carbon or biochar. HTC is the hydrothermal degradation of sustainable precursors under a hot, auto-compressed, aqueous environment and produces both a chemical-rich process water and an amorphous carbon material called hydrothermal carbon. Forming a sophisticated molecular understanding of these amorphous, high molecular weight carbons has always posed a significant challenge. Spectroscopy is typically limited by drawbacks such as poor signal-to-noise ratios, surface-biased results and challenging sample environments. Thus, in-situ measurement of hydrothermal carbon formation is currently missing, and the reported mechanisms of formation involve an amount of postulation. This talk will discuss spectroscopic methods for investigating the development of both pyrolysis carbons and hydrothermal carbons. The bulk carbon chemistry and structure of these materials will be compared and contrasted with respect to their potential applications. 
References:[1]  R.J. White, V. Budarin, R. Luque, J.H. Clark, D.J., Chem. Soc. Rev. 38 (2009) 3401.[2]  M.-M. Titirici, R.J. White, C. Falco, M. Sevilla., Energy Environ. Sci. 5 (2012) 6796.[3]   J. Lehmann, S. Joseph, Biochar for environmental management : An introduction, in: Biochar Environ. Manag. - Sci. Technol., 2nd Editio, Routledge, 2009: pp. 1–12.