## 1 Introduction
Single- and divalent cations (Na\({}^{+}\), K\({}^{+}\), Mg\({}^{2+}\) and Ca\({}^{2+}\)) had little effect on the process. The presence of Cl\({}^{-}\) and SO\({}_{2}\)\({}^{2-}\) anions in the medium contributed to an increase in the rate of degradation of pollutants with high efficiency (85.1% and 88.0%, respectively). In the presence of CO\({}_{3}\)\({}^{2-}\) and Br\({}^{-}\) anions, the efficiency of the processes decreased to 35.5% and 14.7%, respectively [21]. The inhibitory effect of anions in the decomposition of fenantren with manganese oxide octahedral molecular sieve nanorods during sulfate radical-based oxidation was highest in the presence of NO\({}^{2-}\) and PO\({}_{4}\)\({}^{3-}\) ions, followed by Cl\({}^{-}\), NO\({}_{3}\)\({}^{-}\) and CO\({}_{3}\)\({}^{2-}\), and the lowest was with HCO\({}_{3}\)\({}^{-}\)[16]. As for the comparative analysis of the known data on the decomposition of the specific pollutants considered in this review, when comparing ZnO and TiO\({}_{2}\), TiO\({}_{2}\) is more effective for the photocatalytic decomposition of phenol. The estimated decomposition rates of phenol in the presence of TiO\({}_{2}\) and ZnO are \(\sim\)2.5 mg/L/min [17] and \(\sim\)0.03 mg/L/min [21], respectively. The inclusion of ZnO in the NComp of the M.MIL-100(Fe)@ZnO provided a slight improvement in the decomposition rate (\(\sim\)0.04 mg/L/min) [30], but it did not radically change the situation. The loading of catalysts \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\), HS-CuS-HNCs or La\({}_{2}\)CuO\({}_{4}\) (0.75-1.5 g/L) into petroleum-refining wastewater (PRW) [15; 20; 32] during its purification provides the best results in COD removal. For the destruction of PAHs in comparison with other pollutants (Table 1), the lowest process rates were noted: \(\sim\)0.001 mg/L/min for anthraquinone with TiO\({}_{2}\)[18], \(\sim\)0.3 mg/L/min for anthracene with ZnO [19] or with Fe\({}_{3}\)O\({}_{4}\)/Cu\({}_{2}\)O-Ag [24] and \(\sim\)0.3 mg/L/min for acenaphthylene with ZnO/SiO\({}_{2}\)[22]. It should be noted that almost all processes with NCs presented in Table 1 proceed at a pH close to neutral [15; 19; 20; 23; 29; 32] or slightly acidic [21; 27] values and at ambient temperatures, which is important if a further combination of these processes with biocatalytic reactions is assumed. For sulfate radical-based oxidation of phenanthrene in the presence of manganese oxide octahedral molecular sieve nanorods, equally high purification rates of model and real liquid media were achieved at pH 4-11 [16]. The same trend was noted for metal-free photo-Fenton Cl/S with co-doped carbon nitride nanotube clusters (Cl/S-TCN) during oilfield-produced water purification at pH 3-9 [28]. However, the pH value may have an impact on the effectiveness of AOPs in some cases [21; 25; 26; 30]. It was shown that the photocatalytic decomposition of phenol in the presence of ZnO at pH 5 reaches 84.3%, and as the pH increases, the efficiency decreases uniformly, reaching 69.4% at pH 9 [21]. In favor of carrying out processes at pH 2-4, the researchers chose to decompose phenol, biphenyl A and atrazine with M.MIL-100(Fe)@ZnO during heterogenic photocatalysis/H\({}_{2}\)O\({}_{2}\)[30] of PAHs (naphthalene and benzo(g,h,i)perylene) present in wastewater from oil and gas exploration sites. That was performed with nZVI during the Fenton-like oxidation process [26] and with MIL-101(Cr)/Fe3O4-SiO\({}_{2}\) during the photocatalysis [25] for the treatment of oilfield water. Among the processes that differed from AOPs, pyrolysis is known as an approach to the destruction of organic pollutants using NCs [34]. The successful decomposition of oily sludge by ZnFe\({}_{2}\)O\({}_{4}\) (NPs = 30 nm) during three-stage pyrolysis with the activation of NCs by microwaves was shown. The high energy intensity and the realization of some individual stages of the process at high temperatures (up to 300 \({}^{\circ}\)C) should be noted among the disadvantages of this process.