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Zero-dimensional carbon nanomaterials show intriguing potential in the field of unconventional oil resource development for reducing injection pressure and enhancing oil recovery. However, the complicated synthesis procedure, necessity for surfactant and limited understanding of the mechanism impede their practical applications. In this study, novel high-hydrophilic carbon dots (hh-CDs) with an average particle size of 2.54 ± 0.016 nm were facilely synthesized through an electrochemical approach by employing cost-effective petroleum coke as the carbon source, followed by treating with ozone for further oxidation. The abundant surface functional groups render hh-CDs superior hydrophilicity, dispersibility and stability. Core flooding tests show 0.20 wt% hh-CDs nanofluid delivers a prominent pressure-reducing rate of 23.81% and an enhancement in oil recovery of 26.38% without any surfactant. Analytical results of atomic force microscope (AFM) with hydrophobic probe reveal hh-CDs can adsorb on the rock surface to alter the micro-scale wettability from oil-wet to homogeneous water-wet. The hh-CDs can also efficiently reduce the core surface roughness and afford excess disjoining pressure for oil displacement, accounting for the impressive performance. This work provides a feasible oil systemic circulation for the synthesis of versatile surfactant-free carbon dots for boosting injection pressure reduction and enhancing oil recovery in tight oil reservoirs.

Merging photocatalysis with Fenton-like reaction provides a promising synergetic advanced oxidation technology for water treatment, whereas the rational design of efficient cooperative photo-Fenton system still remains a great challenge. In this study, a ternary α-FeOOH/carbon dots/porous g-C3N4 (α-FeOOH/CDs/p-GCN) composite is developed as visible-light-driven heterogeneous photo-Fenton catalyst for contaminated water remediation. α-FeOOH nanorods are in-situ grown on porous g-C3N4 substrates, among which CDs are intercalated as high-speed electron transmission bridges, simultaneously preventing the photogenerated electron-hole recombination and accelerating the Fe3+/Fe2+ redox cycle. The distinctive heterostructure and synergetic catalytic effect endow α-FeOOH/CDs/p-GCN with superior efficiency, reusability, and universality for recalcitrant pollutant elimination, the reaction rate of which is nearly 13.6, 7.3, 3.4, 1.4, and 5.1 times higher than that of α-FeOOH, bulk g-C3N4 (b-GCN), p-GCN, α-FeOOH/p-GCN, and α-FeOOH/CDs/b-GCN, respectively. The FeOOH/CDs/p-GCN also demonstrates excellent tolerance to realistic environmental matrices including deionized water, sea water, river water, wastewater, and underground water. HO• and •O2− radicals are proved to be the predominant contributors in the photo-Fenton system. This work provides an efficient synergetic visible-light-driven photo-Fenton catalyst possessing great potential for practical contaminated water remediation.

The development and optimization of transition metal-based bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical for high-efficient water splitting. Herein, we propose a carbon dots-oriented strategy for fabricating nitrogen-doped carbon dots/fungus-like CoP microsphere composite on Ni foam (CoP-NCDs/NF). Owing to its unique structure and the strong interactions between carbon dots and CoP, the newly developed CoP-NCDs/NF electrode exhibits significantly enhanced HER and OER bifunctional catalytic activities, with overpotentials as low as 103 and 226 mV at a current density of 10 mA cm−2, respectively. Accordingly, the CoP-NCDs/NF displays excellent overall water splitting performance with a low cell voltage of 1.55 V at 10 mA cm−2 and great stability in a two-electrode alkaline electrolyzer. This study provides an alternative pathway on rationally designing and fabricating carbon dots-based materials for high performance water electrolysis and other energy conversion fields.

Transition metal oxides (TMOs) with high theoretical capacities are promising anode candidates for sodium ion batteries (SIBs), which yet suffers from inferior cycling stability and rate capability due to large volume change and sluggish transport kinetics during the sodiation/desodiation processes. Herein, a general strategy is developed to fabricate ultrafine TMOs nanoparticles encapsulated in nitrogen-doped carbon nanofibers (uf-TMOs@N-CNFs, M = Fe, Mn, Zn, etc.) as advanced anodes for SIBs. The uf-TMOs@N-CNFs are facilely synthesized via an in-situ electrospinning and subsequent carbonization strategy, among which polyvinylpyrrolidone (PVP) is employed as an effective dispersant to suppress metal agglomeration and control the size of TMOs. Benefiting from the intimate interaction between ultrafine TMOs and conductive N-CNFs substrates, the uf-TMOs@N-CNFs can efficiently mitigate the aggregation and pulverization of TMOs, facilitate electron/ion transfer, and boost pseudocapacitive charge storage, leading to superior sodium storage performance, including satisfactory reversible capacity, excellent rate capability, and durable cycling stability. Interestingly, the obtained uf-TMOs@N-CNFs membranes also exhibit excellent flexibility to serve as self-supported and flexible electrodes, demonstrating great potential for flexible SIBs. The present work provides a general and feasible method to construct robust and flexible electrodes for energy storage devices.

Electroreduction of carbon dioxide (CO2) to ethylene (C2H4) is one of the most feasible approaches to reduce the carbon emissions and enhance carbon dioxide utilization, whereas the lack of efficient catalysts impedes the scale application. Cuprous oxide (Cu2O) is a promising catalyst for the formation of C2H4 but with unsatisfied selectivity and stability. Herein, we prepared Cu2O/nitrogen-doped carbon shell (Cu2O/NCS) composite and employed it in the production of C2H4 from CO2 electroreduction. The ultra-thin NCS with graphene-like structure was prepared from petroleum asphalt by template method. The cubic Cu2O nanocrystals are uniformly dispersed on the surface of NCS with ca. 150 nm diameters. Cu2O/NCS loaded on glass carbon electrode showed a high faradaic efficiency of C2H4 (24.7%) at −1.3 V (vs. reversible hydrogen electrode) as well as remarkable stability. The excellent performance of Cu2O/NCS is attributed to the high dispersion of cubic Cu2O nanocrystals and the abundant pyridinic-N moieties in NCS. This work provides a new strategy to improve the selectivity and durability of Cu2O for production C2H4 from electrocatalytic CO2 reduction by fabricating composites with nitrogen-doped carbon materials.

Non-noble, high-efficient electrodes with excellent durability are desirable for water splitting. Herein, a facile strategy has been proposed to in-situ grow nitrogen-doped carbon dots (NCDs) decorated Ni3S2 on Ni foam (NCDs/Ni3S2/NF) by hydrothermal treatment of Ni foam in water solution of thiourea and NCDs. Interestingly, coral-like NCDs/Ni3S2/NF composites are unprecedentedly prepared without any templates, where the Ni3S2 nanorods mainly expose {021} high-index facets. The resultant NCDs/Ni3S2/NF composites are directly used as self-supported electrodes for overall water splitting which deliver a current density of 10 mA cm−2 at 1.50 V with excellent durability in 1.0 M KOH solution.