Single-atom catalysts (SACs) have been promising in various catalytic fields, but the controllable synthesis of SACs with high stability remains challenging. Here, we show a robust strategy toward the fabrication of highly efficient and stable SACs based on the “competitive occupancy” of two metal (M) species on graphene oxide (GO). The abundant M1 (Ti) species predominantly occupy more groups of GO, thereby leaving a tiny number of groups in the gaps of the M1 species to combine with M2 (Co2+, etc.) species. Consequently, this guarantees the formation of Co–N4 SACs embedded in 2D TiN/rGO sheets during nitridation. Further, TiN can act as a “spacer” to prevent Co–N4 from aggregation, thereby improving catalyst stability. Co–N4/TiN–rGO exhibits outstanding catalytic performance for the fast conversion of highly concentrated aromatic nitro compounds (∼0.3–2 mM) into amino compounds and excellent recyclability, which is the best among reported catalysts. In contrast, TiN/rGO has no obvious activity, and Co4N–rGO prepared without Ti competition shows poor activity and stability, which indicates the vital role of Co–N4 and TiN for obtaining the remarkable catalytic ability of Co–N4/TiN–rGO. The reaction mechanism is also proposed based on theoretical calculations. The strategy can be used to design Ni (Fe, Cr, Cu)-based SACs.
Haoxu Si,Shuai Zhang,Yaqin Ding,Chongyang Chai,Shuaishuai Zhou,Cuiping Li,Jingwei Zhang,Chunhong Gong
According to the relationship between unit size and wavelength, electromagnetic waves (EMWs) in metacomposites can be effectively absorbed through inherent loss mechanisms. However, limited loss ability has emerged as a primary obstacle to achieving efficient EMW absorption (EMWA) performance. The challenge of enhancing the attenuation of corresponding metacomposites remains important. In this study, we prepared elaborate titanium nitride/reduced graphene oxide units with controllable conductivities and sizes, which formed the microwave antireflective surface of metacomposites. This configuration contributes to improved impedance matching and reduced temperature sensitivity concerning EMWA performance. More importantly, EMWs experience repeated collisions and loss, along with multiple reflections and scattering within metacomposites. This phenomenon extends the transmission pathways of EMWs, thereby increasing additional loss capacity. Consequently, these metacomposites exhibited exceptional EMWA performance across a broad temperature range (298 to 573 K), while maintaining a low filler content of 1.0 wt% units. Henceforth, our findings not only provide an advantageous pathway for high design flexibility in EMWA but also pave the way for new research directions and possibilities regarding advanced lightweight metacomposites that optimize EMWA over an extensive temperature range.
Boqiu Luo,Yiran Han,Tingting Yang,Junyou Li,Hao Wang,Wenjing Chen,Xiaoke Li
Strong solar capture and high heat transfer are extremely vital for designing solar-to-heat absorber to improve photo-thermal conversion efficiency in direct absorption solar collectors (DASCs). In this paper, the plasmonic nanofluids containing reduced graphene oxides (rGO) decorated with titanium nitride (TiN) nanoparticles were prepared. Their superior solar-thermal conversion efficiency and heat transfer property was based on the synergy between the Localized Surface Plasmon Resonances (LSPR) effect of TiN and the high thermal conductivity of rGO. The optical properties of plasmonic nanofluids were investigated with the concentration and penetration depth, which indicated that the existence of TiN on graphene could improve the light-capture ability. The results indicated that the TiN@rGO plasmonic nanofluids could be used for DASCs applications, even under the low mass concentrations. Specifically, the maximum photo-thermal conversion efficiency of the plasmonic nanofluids was 66.74% at 40 ppm concentration, which was about 23% higher than that of pure water. And, the experimental results show that the photothermal conversion efficiency will be reduced if the nanofluid concentration is higher than the optimal concentration. This work exhibited the potential application of plasmonic-graphene nanofluids in DASCs.
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