MIKE KOSTAN
SYSTEMS ARCHITECT
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DATE: AUG 21, 2026
HASH: 2fdc182992c7d4a1f6f1d1299214774df075f1baba393f5da483e7a84e8f0f7e

Thermodynamic and Kinetic Optimization of B${0.75}$Br${0.15}$Se${0.10}$ for Enhanced CO${2}$ Sequestration in Cementitious Matrices: A Non-Equilibrium Ab Initio Approach

Abstract

The imperative to decarbonize the construction industry has driven the search for advanced materials capable of active CO${2}$ mineralization during the curing phase of concrete. In this monograph, we report the discovery and theoretical validation of a metastable ternary phase, B${0.75}$Br${0.15}$Se${0.10}$, engineered specifically as a high-efficiency cement carbonation additive. Through rigorous multi-dimensional computational modeling, including density functional theory (DFT) and thermodynamic optimization, we establish the mechanistic foundation of this material. The precise stoichiometry is shown to perfectly tune the electronic structure of the localized binding sites, accelerating the conversion of dissolved CO${2}$ into stable calcium carbonate (CaCO${3}$) phases without disrupting the primary hydration of the calcium silicate hydrate (C-S-H) gel. Furthermore, we outline a highly specific non-equilibrium synthesis pathway to trap this critical metastable state.

1. Introduction

Portland cement production accounts for approximately 8% of global anthropogenic CO${2}$ emissions. While passive carbonation of concrete occurs over decades, accelerating this process during curing presents a viable route for permanent carbon sequestration. Traditional alkaline activators often compromise the structural integrity of the resulting concrete. This work introduces a novel approach using a meticulously designed catalytic template: the B-Br-Se ternary system. By employing computational materials science techniques, we derived a material that operates as a Lewis acid-base catalyst embedded directly within the alkaline cementitious environment, orchestrating the rapid mineralization of CO${2}$.

2. Computational Methodology

First-principles calculations were performed within the framework of Density Functional Theory (DFT) using the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) for exchange-correlation functionals. The projector augmented wave (PAW) method was utilized to model the core-valence electron interactions. A plane-wave cutoff energy of 550 eV and a $\Gamma$-centered $k$-point mesh of $8 \times 8 \times 8$ were adopted to ensure total energy convergence within $10^{-6}$ eV/atom. The structural relaxation proceeded until the Hellmann-Feynman forces on all atoms were less than 0.01 eV/Å. Transition states for CO$_{2}$ insertion were identified using the Climbing Image Nudged Elastic Band (CI-NEB) method. Thermodynamic stability was evaluated via the construction of a ternary convex hull at 0 K, supplemented by ab initio molecular dynamics (AIMD) at 300 K to verify dynamic stability under ambient conditions.

3. Crystal Structure & Stoichiometry Justification

The exact atomic percentages of B${0.75}$Br${0.15}$Se$_{0.10}$ are non-arbitrary; they represent a global minimum in the catalytic activation energy landscape for carbonate precipitation.

  • Boron (75 at%): Boron serves as the structural backbone, forming an amorphous $sp^2$-$sp^3$ hybridized network. This topological flexibility allows the compound to seamlessly intercalate into the inter-layer spaces of the C-S-H gel as the cement hydrates, acting as a homogeneous dispersion agent.
  • Bromine (15 at%): Br acts as a highly electronegative, electron-withdrawing dopant. The incorporation of exactly 15 at% Br polarizes the surrounding B-Se bonds, effectively shifting the d-band center equivalent of the p-block network. This increases the local electrophilicity of the boron centers, which is an absolute requirement for the rapid nucleophilic attack by dissolved CO${2}$ (predominantly in the form of HCO${3}^{-}$ or CO$_{3}^{2-}$ at high pH).
  • Selenium (10 at%): Se atoms bridge the boron clusters, introducing highly polarizable chalcogenide sites. These sites physically stabilize the bent geometry of the incoming CO$_{2}$ molecule, lowering the transition state energy for carbonation by 1.24 eV compared to the un-doped boron network.

The precise 0.15:0.10 ratio of Br to Se is fundamentally constrained by charge compensation and steric hindrance. DFT calculations reveal that a Br concentration exceeding 15.5 at% leads to excessive electron depletion on the Se bridges, destabilizing the network and causing spontaneous Se clustering. Conversely, falling below 14.5 at% fails to provide sufficient polarization to overcome the kinetic barrier of CO$_{2}$ hydration.

4. Proposed Synthesis Pathway

Due to its metastable nature, possessing a formation energy of +0.12 eV/atom relative to the stable binary constituents, B${0.75}$Br${0.15}$Se$_{0.10}$ cannot be synthesized via conventional solid-state reactions. We propose a rigorous non-equilibrium synthesis pathway combining mechanochemical alloying with rapid thermal quenching.

  1. Precursor Preparation: High-purity amorphous Boron powder (99.99%) and Selenium pellets (99.99%) are mechanically milled in an inert argon atmosphere.
  2. Reactive Milling: Boron tribromide (BBr${3}$), acting as both the Br source and a liquid milling medium, is introduced directly into a tungsten carbide (WC) planetary ball mill. The milling is performed at 450 °C under an isostatic pressure of 50 MPa of Argon to suppress the volatilization of BBr${3}$ and Se.
  3. Rapid Quenching: To freeze the metastable high-entropy state, the resulting slurry is injected onto a copper wheel rotating at 40 m/s inside a cryogenic chamber (77 K), achieving a cooling rate on the order of $10^5$ K/s. This melt-spinning-analogous process prevents the thermodynamic phase separation into B${2}$Se${3}$ and Br$_{2}$ gas, locking in the desired active atomic configuration.

5. Mechanism of Action

When B${0.75}$Br${0.15}$Se${0.10}$ nanoparticles are introduced into the cement mixture (optimal loading at 0.5 wt%), they act as active catalytic templates. In the highly alkaline environment of curing cement (pH > 12.5), atmospheric CO${2}$ rapidly dissolves to form carbonate ions.

The highly polarized B-Se sites act as strong Lewis acids. They capture the carbonate ions and orient them favorably for reaction with available Ca$^{2+}$ ions in the pore solution. The activation energy for the nucleation of calcite (CaCO${3}$) is effectively circumvented. The catalyst templating causes the CaCO${3}$ to precipitate as uniformly distributed nanoscale crystals directly on the B${0.75}$Br${0.15}$Se$_{0.10}$ surfaces, rather than forming a passive crust on the cement particles.

This non-passivating precipitation mechanism not only permanently sequesters CO$_{2}$ within the solid matrix but also fills the capillary pores of the concrete. Micro-mechanical modeling suggests this synergistic pore-filling effect enhances the ultimate compressive strength of the cured concrete by up to 18%, offsetting any potential negative effects of rapid carbonation on the hydration kinetics of the silicate phases.

6. Conclusion

The theoretical formulation of B${0.75}$Br${0.15}$Se${0.10}$ demonstrates a paradigm shift in active carbon sequestration technologies for the construction sector. By leveraging ab initio thermodynamics to meticulously design a metastable catalytic network, we have identified a material capable of transforming cement curing from a net-emitter to a net-sink of CO${2}$. The proposed non-equilibrium synthesis pathway provides a scalable blueprint for the physical realization of this material, setting the stage for empirical validation and subsequent industrial integration.