On the measurement and prediction of graphene production for enabling sustainable photocatalytic processes

Perez-Alvarez, Diego Tomohisa ORCID: 0000-0003-2308-3083 (2025). On the measurement and prediction of graphene production for enabling sustainable photocatalytic processes. University of Birmingham. Ph.D.

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Abstract

Two-dimensional materials (2DMs, such as MoS\(_2\), hBN, gC\(_3\)N\(_4\), graphene) have emerged over the last 20 years with diverse applications in construction, electronics, and energy storage, due to their unique electronic, chemical, optical and mechanical properties. One such application of 2DMs is for sustainable, passive water treatment using photocatalysis. Here, they have shown great promise over traditional catalysts (e.g., TiO2) in treating heavily polluted groundwater using only sunlight as the driving mechanism. Reviewing these advanced visible light active photocatalysts (Chapter 1), show they are often composites of several different materials. In many of these photocatalytic systems, graphene has been demonstrated as an essential component for photocatalytic composites, due to its high conductivity and non-volatility. However, key challenges associated with synthesis of 2DMs remain salient. These include the cost and performance of synthesis techniques, limited knowledge of the mechanisms that drive production, and lack of predictive models that describe large scale manufacture.

One group of 2DMs synthesis techniques with demonstrable ability to upscale is liquid phase exfoliation (LPE) using mechanical force. These techniques function by dispersing a layered material in a fluid, and exposing the mixture to an intense mechanical force. Over time, the intense force destroys the layered material into a spectrum of differently sized particles, ranging from macroscopic agglomerates to few-layered material including nanosheets. LPE is also material agnostic, with the ability to synthesise numerous semi-conducting and conducting 2DMs that can form the building blocks of photocatalysts and their heterostructures. In Chapter 2, a simple exfoliation system consisting of a modified kitchen blender is presented alongside evaluation of the system for producing graphene, which formed the basis for OpenLPE, an open hardware and software platform that can be used by the research community. In Chapter 3, this testbed is used to investigate methods of in situ characterisation of few-layered material concentration and morphology, a process which for nanomaterials is otherwise long and exhaustive requiring many steps to ensure proper separation of nanomaterials. Here, UV-Visible spectroscopic measurements are used to enable quick discrimination between materials, highlighting challenges associated with the use of spectroscopic techniques in highly aerated fluid flows.

As exfoliating methods become more widespread, there are no mathematical models available to industry that describe nanomaterial production at scale. Such models would allow for accurate experimentation and evaluation of potential liquid-phase processes with fewer expensive iterations. To address this, Chapter 4 presents a statistical model of graphite breakup using the population balance approach, demonstrating a prediction of graphite breakage and yield of any size fraction. Further, we examine the applicability of positron emission particle tracking for evaluating the internal flow fields of exfoliating systems, with the intention that these measurements can be taken to physically interpret the system. Collectively, these results and models provide insights on the breakage mechanisms and fluid dynamics that underpin mechanochemical exfoliation processes for 2DMs, and provide direction for the eventual intensification and optimisation at any manufacturing scale.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):