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Formation of environmentally persistent free radicals (EPFRs) on carbonaceous material has aroused increasing research attentions. In terms of metal organic frameworks (MOFs) derivatives, however, scarce studies have dedicated to the relevant aspects. Herein, EPFRs have been detected in Bi-metal organic layers (Bi-MOLs) derivatives. The corresponding g-factors and concentrations of EPFRs on Bi2O3@C by pyrolyzed at different temperatures were 2.0041–2.0046 and 7.04 × 1019-1.77 × 1020 spins/g, respectively. Interestingly, similar EPFRs signals were also monitored in HKUST-1 based and UiO-66 based derivatives. We observed that Bi2O3@C system with the highest EPFRs concentration exhibited superior degradation and mineralization efficiency for phenol and tetracycline. Its excellent photocatalytic performance was mainly attributed to the interaction between the internal EPFRs and photoinduced active species, which promoted more generation of reactive oxygen species (ROS) radicals. This hypothesis was supported by line correlations for EPFRs concentration vs. degradation kinetics in samples pyrolyzed at different temperatures (R2 = 0.946). Most significantly, mechanism investigation combined with DFT calculation indicated that the EPFRs not only promote the generation of 1O2 and •OH via molecular oxygen activation pathway but also provided a possibility of enhancing water oxidation by holes. These findings pave the way for MOFs derivative's implication and insight into the role of EPFRs in photocatalysis.

Over the past few decades, the shortage of water resource has prompted a shift in human concept about waste water: from waste to valuable resource. Utilizing wastewater can not only mitigate water scarcity, but also provide an opportunity for nutrient and energy recovery, further offsetting part of the exploitation of valuable resources. When establishing resource recovery systems of wastewater, the implemented technology and materials should be preferentially considered in order to achieve economically feasible and environmentally responsible solutions. The advantages of biochar in cost, nutrient retention and pollutant adsorption efficiency endow its possibility for resource recovery. Thus, understanding the relationship between biochar and resource recovery is essential to develop the applications of biochar in environment remediation and wastewater utilization. However, to this date there is no comprehensive review that establish the relevance between biochar and recycled substance. In this review, we aim to evaluate the roles of biochar in resource recovery from wastewater. Recyclable substances with the presence of biochar mainly include components, water resource and energy. Viable and effective methods for different recovered targets are classified. In particular, through revealing the interrelationship between biochar production methods and recovered substances, we try to provide the guideline for biochar selection. The re-application and value of recovered substances are also summarized comprehensively. Moreover, the current problems, existing limitations, and promising industrial application value of biochar in resource recovery from water are also put forward. This review can create awareness about the possibility of various options for resources recovery from water with biochar and contribute to further development and demonstration in wastewater treatment.