Strong Light Absorption by sp2 Hybridized Carbon Impurities in Diamond Dust - Preprint

[Geoengineering News]

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=5788557

Authors: Joshin Kumar, Gwan-Yeong Jung, Taveen S. Kapoor, Rohan Mishra, Rajan Chakrabarty

22 November 2025

Abstract

Stratospheric aerosol injection (SAI) using diamond dust has been proposed as a solar radiation management technique to mitigate global warming by scattering incoming solar radiation, offering advantages over sulfur-based aerosols such as reduced ozone depletion and acid rain risks. However, detonation synthesis—the most economical method for large-scale nanodiamond production—inevitably introduces sp2-hybridized carbonaceous impurities, often forming shells around diamond cores, which may enhance shortwave absorption and undermine SRM efficacy. This study employs density functional theory and ab-initio molecular dynamics to model these impurities across hydrogen-to-carbon (H/C) ratios from 0.0 to 1.0, revealing a continuum of optical properties where decreasing sp2 content reduces the imaginary refractive index (k). Particle-scale core-shell Mie scattering simulations at 550 nm for diamond cores of 300 nm diameter with carbonaceous impurity shells (1.95 + ki refractive index, shell thickness of ~0.1–10 nm corresponding to 0.1–10% impurity mass fraction) show that these impurities elevate the effective mass absorption coefficient to up to ~1 m2/g—nearly 15% that of black carbon (~7.5 m2/g)—and decrease single-scattering albedo by up to 25% relative to pure diamond. These absorption enhancements, driven by the k and impurity mass fraction of the shell, could shift diamond dust's radiative forcing toward warming. Our findings highlight the critical need to revisit diamond’s efficacy as an SAI candidate material.

Source: SSRN