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Excessive discharge of TC poses a threat to the environment and human health, while finding a cost-effective treatment method to remove TC from water still remains a challenge. In this study, NH2-MIL-88B(Fe)/TiO2/PAN (NMTP) electrospinning nanofibrous membranes (ENMs) were prepared, and the NMTP ENMs were characterized by SEM, XRD, UV-vis and other characterization methods. The results show that the introduction of NH2-MIL-88B(Fe) expands the photoresponse range of ENMs and improves the hydrophilicity of the membranes, NMTP ENMs exhibit excellent photocatalytic performance during the photocatalytic process, and the best sample has excellent photocatalytic performance for TC. The degradation efficiency can reach 93.0%. After 4 times of photocatalytic regeneration, the removal rate still remains about 80%, and its recovery performance is high. The best degradation efficiency of CTC and OTC can reach 94.9% and 86.5%, respectively. In the oil-water separation experiment, the NMTP ENMs exhibited excellent separation performance and high throughput for oil-in-water emulsions, with separation efficiencies of 98.15%, 97.43% and 84.87% for toluene-in-water, n-heptane-in-water and n-hexane-in-water emulsions, respectively. Based on the above results, this study provides a new strategy for developing efficient and stable technologies for simultaneous catalysis and separation of oil-in-water emulsions.

Purpose This paper aims to design a novel feature descriptor to improve the performance of feature matching in challenge scenes, such as low texture and wide-baseline scenes. Common descriptors are not suitable for low texture scenes and other challenging scenes mainly owing to encoding only one kind of features. The proposed feature descriptor considers multiple features and their locations, which is more expressive. Design/methodology/approach A graph neural network–based descriptors enhancement algorithm for feature matching is proposed. In this paper, point and line features are the primary concerns. In the graph, commonly used descriptors for points and lines constitute the nodes and the edges are determined by the geometric relationship between points and lines. After the graph convolution designed for incomplete join graph, enhanced descriptors are obtained. Findings Experiments are carried out in indoor, outdoor and low texture scenes. The experiments investigate the real-time performance, rotation invariance, scale invariance, viewpoint invariance and noise sensitivity of the descriptors in three types of scenes. The results show that the enhanced descriptors are robust to scene changes and can be used in wide-baseline matching. Originality/value A graph structure is designed to represent multiple features in an image. In the process of building graph structure, the geometric relation between multiple features is used to establish the edges. Furthermore, a novel hybrid descriptor for points and lines is obtained using graph convolutional neural network. This enhanced descriptor has the advantages of both point features and line features in feature matching.

A nanocomposite was synthesized from reduced graphene oxide (rGO), polyaniline (PANI), and carboxymethyl cellulose (CMC) as the initial materials by in situ polymerization. The substrate rGO provides many active sites for in situ polymerization of aniline and self-assembly of CMC. Scanning electron microscopy, X-ray diffraction, thermogravimetry, Raman, Infrared Spectroscopy, and X-ray photoelectron spectroscopies were used to characterize the morphology, electronic structure, and composition of different materials. The nanocomposite was used to modify a glassy carbon electrode (GCE) to obtain a sensor for chiral electrochemical recognition of tryptophan enantiomers. Their electrochemical properties and recognition abilities were investigated using cyclic voltammetry and differential pulse voltammetry, and the final consequence demonstrated that the modified GCE could well distinguish l-tryptophan and d-tryptophan. The enantiomeric selectivity is 2.26. The GCE was successfully used for the recognition of d-tryptophan and l-tryptophan in spiked serum and urine samples.

A Ni-based metal organic framework (Ni-BDC) and subsequently derived NiFe-LDH were studied to overcome the defect of the low availability of active sites for the oxygen evolution reaction (OER) during the water splitting process. This work reported NiFe-LDH nanosheets with an ultra-thin structure through an in situ surface-conversion derived from Ni-BDC. The unique structure and characteristic morphology were confirmed using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy, and the OER activities of the catalysts were systematically studied. The obtained results indicated that the synthesized Ni-BDC@NiFe-LDH-2 showed excellent OER activity, with a low overpotential of 272 mV at a current density of 10 mA cm−2, a small Tafel slope of 45 mV dec−1, and excellent stability, owing to the addition of abundant metal sites and the expansion of the electron transport channels during the conversion process to form the ultra-thin layer structure. This work provides a novel strategy for the application, design, and manufacture of metal organic framework (MOF)-based high-efficiency active materials.

In this work, we invented a new method to synthesize boron- and nitrogen-co-doped graphene quantum dots (B, N-GQDs). This synthesis method was more reliable, simple, and environmentally friendly than the bottom-up methods reported in the current literature that use citric acid or other organic materials as the carbon source. Instead, B, N-GQDs were synthesized from graphene oxide (GO) by a top-down method. The obtained B, N-GQDs showed a bright blue luminescence under a UV lamp at 365 nm, and the absolute photoluminescence quantum yield (PLQY) was 5.13%. Because mercury(II) ions (Hg2+) are highly toxic and can seriously affect the ecological environment and human health, the detection of low-concentration Hg2+ and the establishment of rapid, accurate and sensitive methods for detecting Hg2+ are of great significance to the activities of life, including those of humans. Therefore, using the good luminescence properties of B, N-GQDs, we invented a new type of fluorescence sensor that can detect Hg2+. The sensor was very sensitive to Hg2+, had a good linear relationship in the concentration range of 0.2–1 μM, and exhibited a minimum limit of detection of 6.4 nM. Furthermore, this approach was successfully applied to the detection of Hg2+ in real environmental water samples.

Graphene Quantum Dots (GQDs) are graphene nanoparticles with a particle size of less than 100 nm. GQDs are used as sensitizers for semiconductor catalytic materials and have a significant enhancement effect on the catalytic performance of the catalyst. We have prepared GQDs/CeO2 composites to improve the catalytic performance of CeO2. GQDs in the GQDs/CeO2 composites were uniformly coated around each CeO2 crystal, which effectively increased the reactive sites and effective contact interfaces. The composite GQDs-4.5/CeO2 absorption edge was broadened to 475 nm, with extremely low electron-hole recombination rate and optimal photoelectric performance. The composite material formed a heterogeneous structure with staggered energy levels. The photogenerated electrons were transferred from the GQDs conduction band to the CeO2 conduction band, which effectively prolonged the carrier lifetime, showed enhanced photocatalytic activity, and decomposed Rhodamine B (RhB) photocatalytic reaction under visible light. The reaction rate constant was up to 13.8 times that of pure CeO2.

In this paper, we propose a semantic simultaneous localization and mapping (SLAM) framework for rescue robots, and report its use in navigation tasks. Our framework can generate not only geometric maps in the form of dense point-clouds but also corresponding point-wise semantic labels generated by a semantic segmentation convolutional neural network (CNN). The semantic segmentation CNN is trained using our RGB-D dataset of the RoboCup Rescue-Robot-League (RRL) competition environment. With the help of semantic information, the rescue robot can identify different types of terrains in a complex environment, so as to avoid specific obstacles or to choose routes with better traversability. To reduce the segmentation noise, our approach utilizes depth images to perform filtering on the segmentation results of each frame. The overall semantic map is then further improved in the point-cloud voxels. By accumulating results of multiple frames in the voxels, semantic maps with consistent semantic labels are obtained. To show the advantage of having a semantic map of the environment, we report a case study of how the semantic map can be utilized in a navigation task to reduce the arrival time while ensuring safety. The experimental result shows that our semantic SLAM framework is capable of generating a dense semantic map for the complex RRL competition environment, with which the arrival time of the navigation time is effectively reduced.

The design and preparation of highly efficient and durable non-noble metal electrocatalysts for overall water splitting is pivotal for actualizing large-scale water splitting via electrolysis. Herein, porous Ni0.85Se nanospheres anchored on reduced graphene oxide (RGO) (Ni0.85Se/RGO) were synthesized via a one-step hydrothermal method. Following explorations of the hydrothermal temperature and reaction time, the optimized Ni0.85Se/RGO exhibited extraordinary oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance in 1.0 M KOH solution, providing an overpotential as small as 320 mV at a current density of 30 mA cm−2 and a low Tafel slope of 91 mV dec−1 for the OER, and an overpotential of 169 mV at a current density of 10 mA cm−2 and a low Tafel slope of 65 mV dec−1 for the HER. A current density of 10 mA cm−2 at 1.64 V and high stability can be obtained upon using Ni0.85Se/RGO as both the cathode and anode for overall water splitting under alkaline conditions; this was attributed to the merits of both the porous structure of Ni0.85Se and the high conductivity of RGO. This work provides a meaningful exploration of the synthesis of 3d-transition-metal-chalcogenide- and carbon-based composite electrocatalysts via a hydrothermal reaction for water splitting, and provides a general method.

The design and synthesis of efficient, durable, low-cost catalysts are vital for the oxygen evolution reaction (OER) because it is an important process in energy conversion and storage. Here, we describe the use of a simple hydrothermal process to successfully synthesize novel nitrogen-doped graphene quantum dots (N-GQDs) anchored on NiFe layered double hydroxide sheets (N-GQDs/NiFe-LDH). Structural, morphological, and crystalline phase characteristics were confirmed by applying SEM, TEM, XPS, and XRD studies. These analyses clearly showed the formation of the N-GQDs/NiFe-LDH composite with a hierarchical nanosheet structure possessing higher surface area values and a wide range of pores (10–180 nm). Further study showed that the as-prepared N-GQDs/NiFe-LDH composite exhibited excellent electrocatalytic activity for the OER in alkaline solution, affording small overpotential of 279 and 300 mV at current densities of 20 and 50 mA cm−2, respectively, a low Tafel slope of 47 mV dec−1, and satisfactory stability. The outstanding reactive kinetics outperformed those of most previously reported transition-metal-based catalysts. The excellent OER catalytic activity for the N-GQDs/NiFe-LDH composite is attributed to the synergistic effect of the N-GQDs and NiFe-LDH, the existence of pyridinic-N and graphitic-N on the N-GQDs, and the hierarchical nanosheet and its porous structure. This work provides a new strategy for designing and fabricating novel carbon-based LDH composites.

Given the versatility and value of the semiconductor composites for photocatalysis, we reported a new, friendly environment, high specific surface area material of the graphene quantum dots/hollow titanium dioxide nanosphere (GQDs/H-TiO2) composites which are synthesized through a simple hydrothermal method. GQDs (~ 5 nm) exhibit highly photoluminescent and widely visible light absorption properties. H-TiO2 has high surface area and abundant exposed active sites for photocatalysis. The research demonstrates that GQDs coupled on H-TiO2 can effectively enlarge the light absorption of the H-TiO2 to visible region (~ 650 nm) and enhance the electron–hole pair separation efficiency of GQDs/H-TiO2 composites owing to GQDs acting as an electron repository and electron transport bridge. In our delight, the photocurrent enhancement of newly prepared GQDs-3.0/H-TiO2 composite electrode was almost 3.5 times higher in comparison with that in pure H-TiO2 electrode at an applied voltage of 0.5 V using Na2SO4 (0.5 M) solution as the electrolyte. In addition, the photocatalytic activity of the prepared GQDs-3.0/H-TiO2 (96.9%) on the degradation of Rhodamine B (RhB) was also significantly enhanced compared with that of pure H-TiO2 (33.3%) after 180 min. The protocol is suitable not only for the GQDs-modified semiconductors photocatalysts but also provides further insights to apply GQDs to other energy conversion devices.

A facile approach was reported to synthesize β-cyclodextrin functionalized graphene that is bridged by 3,4,9,10-perylene tetracarboxylic acid (rGO-PTCA-CD) via a chemical route that involves the functionalization of rGO with PTCA followed by covalently cross-linking NH2-β-CD. The as-prepared rGO-PTCA-CD was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical methods. The working electrodes were thoroughly studied for the cyclic voltammetry by using [Fe(CN)6]4−/3- as redox probe and using ferrocene as an internal standard. Furthermore, rGO-PTCA-CD was successfully applied to the recognition of phenylalanine enantiomers. The host-guest inclusion interaction between rGO-PTCA-CD and the phenylalanine enantiomers was investigated by differential pulse voltammetry with Fc used as a competitor. The recognition result showed that the rGO-PTCA-CD-modified glassy carbon electrode exhibited higher chiral recognition capability for L-Phe than for D-Phe with an enantioselectivity coefficient of 2.07. The proposed modified electrode had a limit of detection of 0.08 nM and 0.2 nM (S/N = 3) for L-Phe and D-Phe, respectively, with a linear response range of 0.01 mM to 5 mM, which was ascribed to the synergy of the rGO-PTCA (e.g., its excellent electrochemical performance) and β-CD (e.g., the hydrophobic inner cavity with good molecular recognition and enrichment abilities).

A novel approach for the fabrication of chiral sensing platform via the Michael addition or Schiff base reaction between functionalized graphene with polydopamine (rGO-PDA) and L-lysine (L-Lys) was first put forward. GO can be modified and reduced simultaneously via using dopamine. By utilizing catechol functional group on PDA, L-Lys combined with rGO-PDA via the Michael addition or Schiff base reaction. Michael addition reaction occurred between electrophilic conjugate system (L-Lys) and nucleophilic negative carbon ion (rGO-PDA). We firstly synthesized the L-Lys copper (II) (L-Lys-Cu) complex to protect the chiral sites on L-Lys. The terminal amino group on L-Lys-Cu will interact with rGO-PDA by Michael addition or Schiff base reaction to synthesize rGO-PDA/L-Lys copper (II) composite. The copper ions in rGO-PDA/L-Lys copper (II) composite were removed to prepare rGO-PDA-L-Lys chiral composite, which was served as electroactive materials to discriminate tryptophan (Trp) enantiomers via electrochemical method. The results showed that the rGO-PDA-L-Lys showed better affinity for D-Trp than L-Trp owing to the formation of diastereomeric complexes between enantiomer (D-Trp) and selector (L-Lys). Besides, the proposed rGO-PDA-L-Lys showed great application potential in actual samples.