Dye and nitro-compound pollution has become a significant issue worldwide. The adsorption and degradation of dyes and nitro-compounds have recently become important areas of study. Different methods, such as precipitation, flocculation, ultra-filtration, ion exchange, coagulation, and electro-catalytic degradation have been adopted for the adsorption and degradation of these organic pollutants. Apart from these methods, adsorption, photocatalytic degradation, and chemical degradation are considered the most economical and efficient to control water pollution from dyes and nitro-compounds. In this review, different kinds of dyes and nitro-compounds, and their adverse effects on aquatic organisms and human beings, were summarized in depth. This review article covers the comprehensive analysis of the adsorption of dyes over different materials (porous polymer, carbon-based materials, clay-based materials, layer double hydroxides, metal-organic frameworks, and biosorbents). The mechanism and kinetics of dye adsorption were the central parts of this study. The structures of all the materials mentioned above were discussed, along with their main functional groups responsible for dye adsorption. Removal and degradation methods, such as adsorption, photocatalytic degradation, and chemical degradation of dyes and nitro-compounds were also the main aim of this review article, as well as the materials used for such degradation. The mechanisms of photocatalytic and chemical degradation were also explained comprehensively. Different factors responsible for adsorption, photocatalytic degradation, and chemical degradation were also highlighted. Advantages and disadvantages, as well as economic cost, were also discussed briefly. This review will be beneficial for the reader as it covers all aspects of dye adsorption and the degradation of dyes and nitro-compounds. Future aspects and shortcomings were also part of this review article. There are several review articles on all these topics, but such a comprehensive study has not been performed so far in the literature.

Photothermal water evaporation, benefiting from solar energy, is one hot topic concerning seawater desalination, sewage treatment, and water recovery. Commonly, the photothermal evaporation system consists of photothermal material supported by certain matrices with fundamental necessities. Poly(acrylic acid) (PAAc) cryogels, prepared at the temperature below the freezing point of polymerization mixture, are hierarchically macro-porous and highly hydrophilic with rapid water uptake, speedy water transport, and low thermal conductivity. Moreover, PAAc has the acid-doping ability for polyaniline and polypyrrole (PPy), which faciliates the good incorporation of photothermal materials in a cryogel matrix. Thus, the PAAc cryogel is an excellent platform for photothermal water evaporation. In this research, we prepared PAAc cryogels, incorporated different photothermal materials, and constructed the modular water evaporation systems. The photothermal evaporation rate of pure water with the PAAc-PPy cryogel system reached as high as 1.819 kg m⁻² h⁻¹ while its apparent efficiency surprisingly exceeded 100%. These modular systems exhibited excellent long-term and recyclable utility. As for the photothermal evaporation of salty water, the precipitated salt solid could be spontaneously dissolved during the light turnoff due to the quick water transport, maintaining the high water-to-vapor conversion. This study represents an ideal matrix platform, PAAc cryogel, for photothermal evaporation and opens up a new route to improve the photothermal evaporation technique for water purification and seawater desalination.

Dual thermo- and pH-responsive comb-type grafted hydrogels of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropylacrylamide) (PNIPAM) with reversed network-graft architectures were synthesized by the combination of atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization and click chemistry. Two kinds of macro-cross-linkers with two azido groups at one chain-end and different chain length [PNIPAM–(N₃)₂ and PDMAEMA–(N₃)₂] were prepared with N,N-di(β-azidoethyl) 2-halocarboxylamide as the ATRP initiator. Through RAFT copolymerization of DMAEMA or NIPAM with propargyl acrylate (ProA) using dibenzyltrithiocarbonate as a chain transfer agent, two network precursors with different content of alkynyl side-groups [P(DMAEMA-co-ProA) and P(NIPAM-co-ProA)] were obtained. The subsequent azido-alkynyl click reaction of macro-cross-linkers and network precursors led to the formation of the network-graft hydrogels. These dual stimulus-sensitive hydrogels exhibited rapid response, high swelling ratio and reproducible swelling/de-swelling cycles under different temperatures and pH values. The influences of cross-linkage density and network-graft architecture on the properties of the hydrogels were investigated. The release of ceftriaxone sodium from these hydrogels showed both thermal- and pH-dependence, suggesting the feasibility of these hydrogels as thermo- and pH-dependent drug release devices.

Platinum drugs have emerged as the most active anticancer agents in clinical tumor treatment. Although platinum drugs are typically effective, they induce severe systemic toxicity due to the lack of selective toxicity and targeting ability between cancer and normal cells. Here, we report an approach to develop tumor extracellular pH-sensitive nanoparticle (esNP)-loaded Pt(IV) prodrugs (esNP-Pt) having acid-cleavable amide linkages of 2,3-dimethyl maleamidic acid (DMMA) pendants and GSH-cleavable Pt(IV) pendants in micellar shells, thus attaining dual-stimuli responses at two locations. These DMMA pendants could achieve charge reversal for specific cellular uptake and endosomal/lysosomal escape via cleaving their amide linkages at pH ≤ 6.8. Cellular uptake assays showed that esNP exhibited similar cellular uptake to pH-insensitive nanoparticles (isNP) with succinamic acid (SA) pendants at pH 7.4, while they showed 6-fold cellular uptake as isNP at pH 6.8 and 10-fold cellular uptake as esNP at pH 7.4. The loaded Pt(IV) pendants could be reduced and liberate cisplatin. The release rate and the total amount of cisplatin increased 6-fold under the stimuli of 10 mmol GSH. MTT assays demonstrated that esNP-Pt showed preferential inhibition (∼50% inhibition at pH 6.8 against ∼20% inhibition at pH 7.4), indicating preferential toxicity against tumors and weak systemic toxicity. These esNP-Pt possess many favorable traits for preferential toxicity to cancer cells, such as minimized nonspecific uptake in blood circulation, enhanced cellular uptake at the tumor site in response to the tumor extracellular level of pH, improved intracellular drug delivery to the tumor cell cytoplasm (TCC) and the in situ release of cisplatin in response to TCC reductive potential, which make them promising candidates for cancer therapy.