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Graphdiyne is a newly discovered two-dimensional planar carbon allotrope with highly π-conjugated interactions. This review aims to introduce graphdiyne and describe its similarities and differences with graphene to better understand the graphdiyne.

In recent years, two-dimensional (2D) black phosphorus (BP) has been widely applied in many fields, such as (opto)electronics, transistors, catalysis and biomedical applications due to its large surface area, tunable direct bandgap, superior charge carrier mobility, and unique in-plane anisotropic structure. To exploit its full potential and push the limits, studies on functional 2D BP nanostructures fabricated by a variety of methods, such as surface functionalization and hybridization, are rapidly expanding for next-generation devices with unprecedented properties. In this review, firstly, the synthetic techniques and fundamental properties of functional 2D BP nanostructures, including surface-modified 2D BP nanostructures and mixed-dimensional 2D BP-based heterostructures, are systematically summarized. Secondly, the recent progress of functional 2D BP nanostructures in the fields of energy storage and conversion, (opto) electronics, catalysis, sensors, nonlinear photonics, and biomedical applications is highlighted. Last but not least, the challenges and future opportunities in these emerging areas are discussed. We hope that this review can provide fundamental guidance on new designs of high-performance functional 2D BP nanostructures to meet the growing demand of next-generation devices.

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

In recent years, nanomaterials and nanotechnology have emerged as vital factors in the medical field with a unique contribution to cancer medicine. Given the increasing number of cancer patients, it is necessarily required to develop innovative strategies and therapeutic modalities to tackle hypoxia, which forms a hallmark and great barrier in treating solid tumors. The present review details the challenges in nanotechnology-based hypoxia, targeting the strategies and solutions for better therapeutic performances. The interaction between hypoxia and tumor is firstly introduced. Then, we review the recently developed engineered nanomaterials towards multimodal hypoxia tumor therapies, including chemotherapy, radiotherapy, and sonodynamic treatment. In the next part, we summarize the nanotechnology-based strategies for overcoming hypoxia problems. Finally, current challenges and future directions are proposed for successfully overcoming the hypoxia tumor problems.

Wonderful black phosphorus (BP) and some BP analogs (BPAs) have been increasingly studied for their biomedical applications owing to their fascinating properties and biodegradability, but opportunities and challenges have always coexisted in their study. Poor stability upon exposure to the natural environment is the major obstacle hampering their in vivo applications. BP/polymer and BPAs/polymer nanocomposites can not only efficiently prevent their oxidation and aggregation but also exhibit "biological activity" due to synergistic effects. In this review, we briefly describe the synthesis methods and stability strategies of BP/polymer and BPAs/polymer. Then, advances pertaining to their exciting therapeutic applications in various fields are systematically introduced, such as cancer therapy (phototherapy, drug delivery, and synergistic immunotherapy), bone regeneration, and neurogenesis. Some challenges for future clinical trials and possible directions for further study are finally discussed.

The exfoliation of phosphorene from black phosphorus to afford mono-elemental two-dimensional (2D) materials (Xenes) has caused a boom in various fields since 2014. Among the Xenes, an emerging class of material, 2D pnictogens, which includes phosphorene, arsenene, antimonene, and bismuthene, has drawn a great deal of attention in the field of catalysis owing to their high specific surface area, mechanical properties, biocompatibility, and optical and electrical performance. With the development of interdisciplinary research, it has become a new trend of scientific research, especially the application of catalysis in medicine, to break the barriers between disciplines and achieve multidisciplinary joint investigation. Herein, firstly, the structures, general properties, and synthetic methods of 2D pnictogen (group VA) materials are reviewed. Then, we summarize the various state-of-the-art catalytic applications of the 2D pnictogen family, such as photocatalysis, electrocatalysis, and medical catalysis, especially in terms of strategies to improve their catalytic performance, such as doping, functionalization, and heterostructures. We also shed some light on the cross-subject of photocatalytic and electrocatalytic processes for biomedical applications. Finally, we summarize the research progress, outlooks, and challenges for these 2D catalysts in terms of their catalytic performance, characterization, reaction mechanisms, exploration of new systems, and commercial applications. This review aims to highlight the catalytic effects of 2D pnictogen materials in enhancing the performance of reactions.

As promising non-volatile memory devices, memristors have received extensive attention since they can effectively mimic synapses and enable the fabrication of neuromorphic systems. In recent years, 2D materials have been widely used in memristors because of their unique advantages, which not only improve the performance of memristors, but also promote the applicability of memristors in flexible electronics, low-power high-temperature devices, neuromorphic computing, etc. In this review, we summarize the applications of 2D materials in fabricating memristors and their physical switching mechanisms. The challenges involved are discussed and the corresponding strategies are reviewed.

Two-dimensional (2D) inorganic nanomaterials for biomedical applications still face the challenge of simultaneously offering a high photothermal conversion efficiency (PTCE), efficient drug delivery, biocompatibility and biodegradability. Herein, cancer treatment using tin sulfide nanosheet (SnS NS)-based dual therapy nano-platforms (SDTNPs), including photothermal- and chemo-therapy, is demonstrated. SnS, a black phosphorus (BP) analogue binary IV-VI compound, was synthesized using liquid phase exfoliation. SnS NSs comprising 2-4 layers exhibited good biocompatibility and a high PTCE of 39.3%, which is higher than other popular 2D materials. The SnS NSs showed a stable photothermal performance over 2 h of laser irradiation and exhibited ∼14% degradation after 10 h of irradiation. It was also found that SnS NSs show high loading of small molecules such as doxorubicin (DOX) (up to ∼200% in weight). Consequently, the SDTNPs achieved notable tumor therapy through the combination of photothermal- and chemo-therapy both in vitro and in vivo. Our study may pave the way for the biomedical application of SnS and other IV-VI compound-based 2D nanomaterials. Compared with traditional therapies, SnS NS-based laser therapy is green and efficient, due to its biocompatibility, photo-degradability, high efficiency photothermal properties and high drug loading.