The non-aqueous synthesis of shape controllable Cu_2−xS plasmonic nanostructures in a continuous-flow millifluidic chip for the generation of photo-induced heating

Abstract

In this paper, a new method for synthesizing non-aqueous copper sulfide nanocrystals with different shapes and sizes using a homemade continuous-flow millifluidic chip is presented. Conventionally, the shape control of nanocrystals was accomplished using a surfactant-controlled approach, where directional growth is facilitated by selective passivation of a particular facet of the nanocrystals using surfactants. We demonstrate a "surfactant-free" approach where different sizes and shapes (i.e. spherical, triangular prism and rod) of plasmonic copper sulfide (Cu(2-x)S) nanocrystals can be fabricated by adjusting the flow rate and precursor concentrations. As continuous-flow synthesis enables uniform heating and easy variation of precursors' stoichiometries, it serves as an excellent incubation platform for nanoparticles due to its simplicity and high reproducibility. Transmission electron microscopy (TEM), fast Fourier transform (FFT) and X-ray diffraction (XRD) techniques were used to characterize the as-synthesized nanocrystals and revealed structures ranging from copper-deficient covellite (CuS), spionkopite (Cu1.39S), roxbyite (Cu1.75S), to copper-rich djurleite (Cu1.94S). The localized surface plasmon resonance (LSPR) peak of the nanocrystals can be tuned from 1115 to 1644 nm by simply varying the copper to sulfur molar ratio and flow rate. Furthermore, photothermal effects of Cu(2-x)S nanocrystals were also demonstrated to annihilate the RAW264.7 cells upon near infra-red laser irradiation.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting

“…Next, we distinguish the effect of LSPR absorption on final performance from that of intrinsic absorption. As shown in Figure b, the light absorption of the SD sample can be fitted and resolved into two parts, that is, intrinsic absorption (λ < 1180 nm) and LSPR absorption (λ > 760 nm), by comparing the absorption spectra of SD‐NFAs with that of DF‐NFAs, such absorption ranges are well consistent with these reported in literature . Moreover, the intrinsic and plasma absorption ranges overlap in a rather large wavelength range (760–1180 nm), which is a prerequisite for LSPR to work efficiently .…”

Microfluidic Synthesis and Biological Evaluation of Photothermal Biodegradable Copper Sulfide Nanoparticles

“…However, nonaqueous copper sulfide nanocrystals obtained from a continuous-flow millifluidic chip exerted higher cytotoxic effects, decreasing viability to 50% at lower concentrations (<0.003 mg/mL) in RAW264.7 mouse macrophages which was more pronounced when cells were irradiated by a NIR laser due to the photothermal effects of CuS nanocrystals. 35 …”

Synthesis of CuxS Thin Films with Tunable Localized Surface Plasmon Resonances

“…Depending on the synthesis method and experimental conditions, Cu x S forms different phases with a varying stoichiometry between Cu and S. Generally, Cu x S exists as stable chalcocite Cu 2 S and covellite CuS phases, and several stable and metastable phases with varying stoichiometries between those of stable Cu 2 S and CuS . At least nine different Cu x S phases with different compositions and crystal structures have been identified, including villamaninite (CuS 2 ), covellite (CuS), yarrowite (Cu 1.12 S), spionkopite (Cu 1.39 S), geerite (Cu 1.6 S), anilite (Cu 1.75 S), digenite (Cu 1.8 S), djurleite (Cu 1.96 S), and chalcocite (Cu 2 S) . Among the various Cu x S materials, covellite CuS has the highest concentration of hole density of ∼10 21 cm –3 and the highest copper deficiency exhibiting strong p‐type metallic character.…”

“…al; the XRD patterns of the samples for the intermediate Cu 1.3 S and Cu 1.5 S compositions resembled (albeit not completely) those of the initial covellite CuS with a slight decrease in the XRD peak intensity because of the greater amount of copper in the lattice. Based on these observations, the diffraction pattern shown in Figure g was assigned to spionkopite Cu 1.39 S with the corresponding standard JCPDS file No. 36–0380, and having a slight resemblance to that of covellite CuS.…”