Correction: Rechargeable Zn2+/Al3+ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes

Correction for ‘Rechargeable Zn²⁺/Al³⁺ dual-ion electrochromic device with long life time utilizing dimethyl sulfoxide (DMSO)-nanocluster modified hydrogel electrolytes’ by Hopmann Eric et al., RSC Adv., 2019, 9, 32047–32057.

The corrected author listing (first/last) names is shown above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: A highly selective fluorescent probe for human NAD(P)H:quinone oxidoreductase 1 (hNQO1) detection and imaging in living tumor cells

Correction for ‘A highly selective fluorescent probe for human NAD(P)H:quinone oxidoreductase 1 (hNQO1) detection and imaging in living tumor cells’ by Ya Zhu et al., RSC Adv., 2019, 9, 26729–26733.

The authors regret that some articles reporting probes for detecting human NAD(P)H:quinone oxidoreductase 1 were not cited in the original article. The missing references are listed below as ref. 1–6, and should be cited in the original paper at the end of the following sentence on page 26729:Herein, we designed and synthesized a novel fluorescent probe 1 for detection of hNQO1 based on TCF-OH as a chromophore and quinone propionic acid (QPA) as a recognition group.^1–6The authors sincerely apologise for this oversight.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Aggregation-induced emission enhancement (AIEE)-active tetraphenylethene (TPE)-based chemosensor for Hg2+ with solvatochromism and cell imaging characteristics

An aggregation-induced emission enhancement (AIEE)-active fluorescent sensor based on a tetraphenylethene (TPE) unit has been successfully designed and synthesized. Interestingly, the luminogen could detect Hg²⁺ with high selectivity in an acetonitrile solution without interference from other competitive metal ions, and the detection limit was 7.46 × 10⁻⁶ mol L⁻¹. Furthermore, the luminogen also showed interesting solvatochromic behavior and superior cell imaging performance.

A TPE-based AIEE-active fluorescent sensor for Hg²⁺ was synthesized. Furthermore, it showed solvatochromism and cell imaging characteristics.

The design and synthesis of molecular sensors for the detection of metal ions, especially transition-metal ions, has attracted much attention.^1–3 Among all transition-metal ions, mercury (Hg²⁺) is identified as one of the most dangerous and ubiquitous heavy metals. Indeed, it is not biodegradable, and can cause extreme injury to the environment as well as human health.^4–8 Additionally, it can be accumulated through the food chain in the human body, consequently giving rise to several deleterious effects such as central nervous system defects, kidney damage, endocrine system disease and so on.^9–12 Although many governments around the world have adopted strict regulations to limit Hg²⁺ emission, the global Hg²⁺ pollution caused by human activities is still serious.^13,14 Therefore, it is highly desirable to develop a new method for the detection of Hg²⁺ with high selectivity and sensitivity.^15–17Most traditional fluorescent sensors suffer from a detrimental phenomenon called aggregation-caused quenching (ACQ), which usually results in a poor solid-state emission efficiency. Fortunately, in 2001, Tang et al. reported a fluorescent molecule named 1-methyl-1,2,3,4,5-pentaphenylsilole. Interestingly, the fluorescence emission of this luminogen was induced by aggregation, a phenomenon referred to as aggregation-induced emission (AIE).¹⁸ Subsequently, in 2002, Park et al. reported an interesting phenomenon named aggregation-induced emission enhancement (AIEE).¹⁹ In fact, both AIE and AIEE can achieve highly efficient emission in the solid state or aggregated state.^20–27 In the past years, AIE (or AIEE) phenomenon has attracted considerable research interest owing to the potential applications in a lot of fields, including bioimaging, fluorescence sensors, organic lighting emitting diode (OLED) devices and organic lasers.^28–33 Meanwhile, many stimuli-responsive materials have been reported, including photochromism, mechanochromism, and solvatochromism.^34–46 At present, the solvatochromism materials have been generally used in chemical and biological systems.⁴⁷ To date, many fluorescent chemosensors for Hg²⁺ have been reported. In contrast, the corresponding chemosensors with AIE or AIEE effect are rare, not to mention solvatochromic AIE or AIEE-active fluorescent sensors for Hg²⁺ with good cell imaging behavior. Indeed, preparing such multifunctional sensors is challenging and significative. In this paper, we reported an AIEE-active tetraphenylethene (TPE)-based fluorescent sensor (Scheme 1) for the detection of Hg²⁺. Furthermore, the luminogen also showed remarkable solvatochromism and good cell imaging characteristics.Open in a separate windowScheme 1The synthetic route of luminogen 1.To investigate the AIEE phenomenon of luminogen 1, we initially studied the UV-visible absorption spectra and photoluminescence (PL) spectra in acetonitrile–water mixtures with different water fractions (f_w). The results indicated that the absorption spectra exhibited level-off tails in the long wavelength region as the water content increased (Fig. S1^†). It is well-known that such tails are usually associated with the Mie scattering effect, which is the key signal of nano-aggregate formation.^48,49 As presented in Fig. 1, luminogen 1 showed weak fluorescence and the luminescence quantum yield (Φ) was as low as 1.35%. Interestingly, when the f_w in the acetonitrile solution was increased to 80%, an obvious emission band was formed, and a yellow-green fluorescence was observed. As the water content was increased to 90%, the emission intensity was further increased, and a bright yellow-green luminescence (Φ = 27.81%) with a λ_max at 545 nm could be observed.Open in a separate windowFig. 1(a) Fluorescence spectra of the dilute solutions of 1 (2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile–water mixtures with different water content (0–90%). Excitation wavelength = 380 nm. (b) Changes the emission intensity of 1 at 545 nm in acetonitrile–water mixtures with different volume fractions of water (0–90%). (c) PL images of 1 (2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile–water mixtures with different f_w values under 365 nm UV illumination.Clearly, water is a poor solvent of luminogen 1. As a result, the generation of the yellow-green emission can be attributed to the aggregate formation.^50–52 Moreover, as shown in Fig. 2, the nano-aggregates obtained were verified by dynamic light scatterings (DLS). Therefore, 1 is a typical AIEE-active fluorescent molecule, and its AIEE behavior is caused by the restricted intramolecular rotation. As shown in Fig. S2,^† solid-state compound 1 showed a strong green emission (Φ = 14.50%) with a λ_max at 497 nm, and the corresponding fluorescence lifetime is 2.66 ns (Fig. S3^†).Open in a separate windowFig. 2Size distribution curve of luminogen 1 (2.0 × 10⁻⁵ mol L⁻¹) in acetonitrile–water mixtures with f_w = 90%.On the other hand, the luminogen 1 also displayed interesting solvatochromism effect. As presented in Fig. 3, the absorption spectra and fluorescence spectra of luminogen 1 in different solvents were investigated, respectively. Obviously, the absorption spectra was barely affected by the polarity of solvents. However, the photoluminescence peaks were gradually red-shifted from 515 nm to 625 nm, and thus 1 exhibited remarkable solvatochromism behavior. Obviously, the molecular structure of luminogen 1 is distorted due to the presence of TPE unit, and the conjugation degree of molecule 1 is different in various solvents, and the intramolecular charge transfer (ICT) effect is possibly responsible for the solvatochromism behavior of 1.Open in a separate windowFig. 3(a) UV-Vis absorption spectra and (b) normalized fluorescence spectra (Excitation wavelength = 380 nm) of luminogen 1 in different solvents (2.0 × 10⁻⁵ mol L⁻¹). (c) Photographs of 1 under 365 nm UV illumination in different solvents: tol (toluene); THF (tetrahydrofuran); EA (ethyl acetate); BT (acetone); MeCN (acetonitrile); DMSO (dimethyl sulfoxide).Subsequently, the changes in the fluorescence of luminogen 1 induced by Hg²⁺ were investigated in acetonitrile (2.0 × 10⁻⁵ mol L⁻¹) at room temperature. In the fluorometric titration experiments, as shown in Fig. 4, the emission intensity significantly decreased when the Hg²⁺ concentration increased from 0 to 7.0 equivalents in acetonitrile. Meanwhile, the fluorescent color changed from orange-red to colorless, and followed by a plateau upon further titration (Fig. 5). Remarkably, the emission intensity of luminogen 1 was almost quenched completely. Furthermore, based on the titration experiments, the detection limit of luminogen 1 for Hg²⁺ on the basis of LOD = 3 × σ/B (where σ is the standard deviation of blank sample and B is the slope between the fluorescence intensity versus Hg²⁺ concentration) was 7.46 × 10⁻⁶ M (Fig. S4^†). Moreover, a good linear relationship could be obtained (R = −0.9933) and the quenching constant of luminogen 1 with Hg²⁺ was 1.9 × 10⁴ M⁻¹ (Fig. S5^†). On the other hand, the binding ratio of luminogen 1 for Hg²⁺ was established through Job''s plot and the results showed 1 : 1 stoichiometric complexation (Fig. S6^†). Next, the binding interactions between 1 and Hg²⁺ were further investigated by NMR in acetonitrile-d₃. As presented in Fig. 6, the signal of Ha from 9.42 ppm shifted to 9.62 ppm and the Hb changed from 8.43 ppm to 9.24 ppm. Besides, the Hc or Hd was slightly shifted for 0.04 ppm or 0.06 ppm, respectively. These consequences revealed that the N on the pyridine and the N on the pyrazine (near the N on the pyridine) are the most probable binding with Hg²⁺. Mass spectra were utilized to further demonstrate the binding mode of luminogen 1 toward Hg²⁺. The peak located at m/z = 820.0 was coincided well with the ensemble [1 + Hg²⁺ +2NO₃⁻ + Cl⁻]⁻, confirming the binding ratio of luminogen 1 for Hg²⁺ with 1 : 1 stoichiometry (Fig. S7^†).Open in a separate windowFig. 4Fluorescence titration spectra of luminogen 1 (2.0 × 10⁻⁵ mol L⁻¹) induced by Hg²⁺ (0–7.0 equiv.) in an acetonitrile solution. Excitation wavelength = 380 nm.Open in a separate windowFig. 5The emission intensity changes of luminogen 1 at 625 nm with different equivalents of Hg²⁺.Open in a separate windowFig. 6 ¹H NMR (acetonitrile-d₃, 400 MHz) spectra changes of luminogen 1 in the presence of Hg²⁺.Next, in order to study the selectivity behavior of luminogen 1 as a fluorescent sensor for Hg²⁺, other metal ions, such as Zn²⁺, Cd²⁺, Ba²⁺, Sr²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, Al³⁺, Fe³⁺, Cr³⁺, Ag⁺ and K⁺ were also measured in acetonitrile under the same experimental conditions. The corresponding UV-Vis absorption spectra were shown in Fig. S8.^† Furthermore, as showed in Fig. 7, when these cations were added separately into the solution containing luminogen 1, no obvious fluorescence changes were observed. Indeed, as noticed in Fig. S9,^† no obvious interference was observed when Hg²⁺ (7.0 equiv.) was added with other ions (7.0 equiv.). These results indicated that luminogen 1 could be served as a highly selective fluorescent sensor for detection of Hg²⁺.Open in a separate windowFig. 7(a) Fluorescence spectra of luminogen 1 (2.0 × 10⁻⁵ mol L⁻¹) towards various cations including Zn²⁺, Cd²⁺, Hg²⁺, Ba²⁺, Sr²⁺, Mn²⁺, Mg²⁺, Ca²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, Al³⁺, Fe³⁺, Cr³⁺, Ag⁺ and K⁺. Excitation wavelength = 380 nm. (b) Fluorescence photographs of luminogen 1 after addition of various metal ions (7.0 equiv.) under 365 nm light.Fluorescent probe is a powerful tool for optical imaging, which allows direct visualization of biological analytes.⁵³ Luminogen 1 was AIEE-active due to the restriction of intramolecular rotation in the aggregate state, which is beneficial for cell imaging. Indeed, the viability of HeLa cells incubated with luminogen 1 was evaluated by the standard MTT method (Fig. 8), and the result indicated that compound 1 exhibited low cytotoxicity. Next, cell imaging behavior of luminogen 1 was investigated using a confocal laser scanning microscopy (CLSM). HeLa cells were incubated with luminogen 1 (20 μM) for 30 min at 37 °C and the fluorescence images were obtained by CLSM.Open in a separate windowFig. 8The MTT assay of compound 1 for measuring cell viability.As presented in Fig. 9, an intense yellow-green fluorescence, which was consistent with the fluorescence of luminogen 1 in acetonitrile–water mixture with high water content (80% or 90%), was displayed inside the cells. This result indicated that luminogen 1 tended to aggregate inside the cells, and thus the bright yellow-green luminescence was clearly observed. Furthermore, the merged picture c demonstrated that picture a and picture b overlapped very well. These results indicated that luminogen 1 showed superior cell imaging performance.Open in a separate windowFig. 9Fluorescence images of HeLa cells incubated with luminogen 1 (20 μM) for 30 min at 37 °C: (a) bright field image; (b) fluorescence image; (c) merge image (a and b).In summary, a TPE-based fluorescent molecule was designed and synthesized. The luminogen exhibited obvious AIEE phenomenon. Moreover, luminogen 1 could be used as a highly selective fluorescence turn-off chemosensor for Hg²⁺, and the detection limit was 7.46 × 10⁻⁶ mol L⁻¹. Furthermore, 1 also displayed interesting solvatochromic behavior and superior cell imaging performance. Further studies on the design of new AIE or AIEE-active fluorescent chemosensors are in progress.     

Correction: An efficient multicomponent synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed by a magnetic nanoparticle supported Lewis acidic deep eutectic solvent

Correction for ‘An efficient multicomponent synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles catalyzed by a magnetic nanoparticle supported Lewis acidic deep eutectic solvent’ by Thanh Thi Nguyen et al., RSC Adv., 2019, 9, 38148–38153, DOI: 10.1039/C9RA08074K.

The authors apologise that a related reference, given here as ref. 1–5, was not cited in the original article. On page 38148, in the first paragraph of the Introduction, a citation to the reference should be added at the end of the sentence beginning “Among them, Lewis acidic…”. The paragraph should be changed as follows “In past decade, deep eutectic solvents (DESs) have attracted much attention in both reaction media and catalysts due to their unique properties such as wide liquid range, biodegradability, excellent thermal stability, and negligible vapor pressure.^1,2 Among them, Lewis acidic deep eutectic solvents (LADESs) have been intensively studied as efficient media for organic syntheses.^3–5”.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Synthesis and characterizations of YZ-BDC:Eu3+,Tb3+ nanothermometers for luminescence-based temperature sensing

Correction for ‘Synthesis and characterizations of YZ-BDC:Eu³⁺,Tb³⁺ nanothermometers for luminescence-based temperature sensing’ by Lam Thi Kieu Giang et al., RSC Adv., 2022, 12, 13065–13073, https://doi.org/10.1039/D2RA01759H.

The authors regret the omission of a funding acknowledgement in the original article. This acknowledgement is given below.Karolina Trejgis is supported by the Foundation for Polish Science (FNP).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Effects of water,ammonia and formic acid on HO2 + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step

Correction for ‘Effects of water, ammonia and formic acid on HO₂ + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step’ by Tianlei Zhang et al., RSC Adv., 2019, 9, 21544–21556.

The authors regret that incorrect details were given for ref. 52 in the original article. The correct version of ref. 52 is given below as ref. 1.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Nano N-TiO2 mediated selective photocatalytic synthesis of quinaldines from nitrobenzenes

Correction for ‘Nano N-TiO₂ mediated selective photocatalytic synthesis of quinaldines from nitrobenzenes’ by Kaliyamoorthy Selvam et al., RSC Adv., 2012, 2, 2848–2855, DOI: 10.1039/C2RA01178F.

The authors regret omitting citations of their related papers in Journal of Molecular Catalysis A: Chemical and Applied Catalysis A: General: ‘Cost effective one-pot photocatalytic synthesis of quinaldines from nitroarenes by silver loaded TiO₂’ (DOI: 10.1016/j.molcata.2011.09.014)¹ and ‘Mesoporous nitrogen doped nano titania—A green photocatalyst for the effective reductive cleavage of azoxybenzenes to amines or 2-phenyl indazoles in methanol’ (DOI: 10.1016/j.apcata.2011.11.011).² The citations should have appeared in the following places as ref. 36 (ref. 1, in the reference list here) and ref. 37 (ref. 2, in the reference list here):In the sentence starting on line 5 of paragraph 5 in the introduction:‘Photocatalytic synthesis of quinolone derivatives from nitrobenzene using TiO₂, metal doped TiO₂ and others had been reported earlier.^1,23–25’At the end of Section 3.12 with the addition of the following sentence:‘This catalyst was also found to be effective for the reductive cleavage of azoxybenzenes to amines or 2-phenyl indazoles in methanol.²’The authors regret that it was not clear in the original article that the bare TiO₂ and N-TiO₂ characterisation data had been reproduced from their related Journal of Molecular Catalysis A: Chemical, Applied Catalysis A: General and Catalysis Communications papers.^1–3 Although the Catalysis Communications article was cited as ref. 25 (ref. 3, in the reference list here) in the original article, it was not made clear that some of the data was reproduced from this article. The appropriate figure captions have been updated to reflect this.Fig. 2: Diffuse reflectance spectra of (a) bare TiO₂, (b) N-TiO₂ and (c) TiO₂-P25. The bare TiO₂ data in Fig. 2a have been reproduced with permission from ref. 1. Copyright 2011 Elsevier. The N-TiO₂ data in Fig. 2b have been reproduced with permission from ref. 2. Copyright 2012 Elsevier.Fig. 3: Photoluminescence spectra of (a) bare TiO₂, (b) TiO₂-P25 and (c) N-TiO₂. The bare TiO₂ data in Fig. 3a have been reproduced with permission from ref. 1. Copyright 2011 Elsevier. The N-TiO₂ data in Fig. 3c have been reproduced with permission from ref. 2. Copyright 2012 Elsevier.Fig. 4: HR-TEM analysis: (a and b) images at two different regions of N-TiO₂, (c) SAED pattern of N-TiO₂, (d) lattice fringes of N-TiO₂ and (e) particle size distribution of N-TiO₂. Fig. 4 has been entirely reproduced with permission from ref. 2. Copyright 2012 Elsevier.Fig. 5: X-ray photoelectron spectra of N-TiO₂: (a) survey spectrum, (b) Ti 2p peak, (c) O 1s peak, (d) N 1s peak and (e) C peak. Fig. 5 has been entirely reproduced with permission from ref. 2. Copyright 2012 Elsevier.Fig. 6: (a) N₂ adsorption–desorption isotherms of N-TiO₂ and (b) its pore size distribution. Fig. 6 has been entirely reproduced with permission from ref. 2. Copyright 2012 Elsevier.Fig. 8: GC-MS chromatograms at different reaction times for the photocatalytic conversion of nitrobenzene with N-TiO₂. Fig. 8 has been entirely reproduced with permission from ref. 3. Copyright 2011 Elsevier.The authors also wish to remove Fig. 1 from the original article due to similarities between two of the spectra and the raw data no longer being available. This does not affect the conclusions as the presence of nitrogen was confirmed by other techniques.The authors also wish to clarify the differences between this RSC Advances paper and the Journal of Molecular Catalysis A: Chemical, Applied Catalysis A: General and Catalysis Communications papers.^1–3 The Journal of Molecular Catalysis A: Chemical paper discusses the photocatalytic synthesis of quinaldines from nitroarenes by silver loaded TiO₂.¹ The Applied Catalysis A: General paper reports the reductive cleavage of azoxybenzenes to amines or 2-phenyl indazoles using mesoporous nitrogen doped nano titania.² The Catalysis Communications paper, ref. 25 in the original article, discusses the synthesis of quinaldines from nitroarenes with gold loaded TiO₂ nanoparticles.³ The original RSC Advances paper discusses the catalytic ability of N-TiO₂ in the synthesis of quinaldines from nitrobenzenes. In each paper, either a different catalyst was used or a different synthetic reaction was investigated.     

Correction: Electrochemical behaviour and analysis of Zn and Zn–Ni alloy anti-corrosive coatings deposited from citrate baths

Correction for ‘Electrochemical behaviour and analysis of Zn and Zn–Ni alloy anti-corrosive coatings deposited from citrate baths’ by Shams Anwar et al., RSC Adv., 2018, 8, 28861–28873, DOI: 10.1039/C8RA04650F.

The authors regret a mistake in the author names of ref. 44. The correct reference is shown below as ref. 1.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Photoelectrochemical study of carbon-modified p-type Cu2O nanoneedles and n-type TiO2−x nanorods for Z-scheme solar water splitting in a tandem cell configuration

Correction for ‘Photoelectrochemical study of carbon-modified p-type Cu₂O nanoneedles and n-type TiO_2−x nanorods for Z-scheme solar water splitting in a tandem cell configuration’ by Nelly Kaneza et al., RSC Adv., 2019, 9, 13576–13585.

The authors regret that eqn (3) is shown incorrectly in the original article. The correct equation is shown here.3The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Synthesis of Bi2WO6/Na-bentonite composites for photocatalytic oxidation of arsenic(iii) under simulated sunlight

Correction for ‘Synthesis of Bi₂WO₆/Na-bentonite composites for photocatalytic oxidation of arsenic(iii) under simulated sunlight’ by Quancheng Yang et al., RSC Adv., 2019, 9, 29689–29698.

Ref. 28 in the published article was incorrect, with an incorrect page range provided. The correct version is shown as ref. 1 below.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: A highly selective ratiometric fluorescent probe for the cascade detection of Zn2+ and H2PO4− and its application in living cell imaging

Correction for ‘A highly selective ratiometric fluorescent probe for the cascade detection of Zn²⁺ and H₂PO₄⁻ and its application in living cell imaging’ by Kui Du et al., RSC Adv., 2017, 7, 40615–40620.

Affiliation c was incomplete in the original publication; the corrected version is shown below.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

A cascade reaction-based switch-on fluorescent sensor for Ce(iv) ions in real samples

We herein report a cascade reaction-based switch-on fluorescence sensor for Ce(iv) ions. The mechanism is based on the ability of Ce(iv) ions to oxidize β-naphthol, which condenses with o-phenylenediamine to generate fluorescent benzo[a]phenazine. The sensor achieved a 200-fold fluorescence enhancement and was successfully applied to real sample detection.

A cascade reaction-based switch-on fluorescent sensor for Ce(iv) ions in river water and soil samples is presented.

Cerium (Ce) is the most abundant rare-Earth element and has been widely used as polishing powders, fluorescent powders, magnets, catalysts and a ceramic colorant in industry.^1,2 Although Ce(iii) is the most abundant type of cerium in the Earth, Ce(iv) can be more easily extracted and separated from cerium fluorocarbonate mineral. Furthermore, the oxidation processes to convert Ce(iii) to Ce(iv) during the post-treatment stage further increases the exposure of Ce(iv) to the community.^3–5 High concentration of Ce is known to be an environmental hazard and to have acute toxicity to seeds.^6,7 Prolonged exposure to Ce(iv) ions will cause malfunctions in the human body, particularly with the circulation systems, immune systems and central nervous systems.⁸ Therefore, accurate and rapid determination of Ce(iv) ion is of significant interest for both environmental and clinical applications.Over the centuries, instrument-based methods have been employed for detection of the Ce(iv) ion, such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), radiochemical neutron activation, and electrochemical methods.^9,10 However, these methods generally have drawbacks including high cost, long processing time, complicated sample preparation and instrumental complexity. Meanwhile, fluorescent sensors are powerful tools for detecting environmentally and biologically significant analytes in the presence of interfering matrices, by virtue of their simplicity and high sensitivity.^11–20 To date, a wide variety of fluorescent sensors have been developed for monitoring Ce ions.^21–25 However, these methods are typically limited by the uses of toxic inorganic nanomaterials, low sensitivity and low selectivity. Therefore, the development of a fast, sensitive and efficient sensing platform for Ce(iv) ions is highly desirable.Over the past years, fluorescence properties of benzo[a]phenazine and its derivatives have received considerable attention in organic synthesis, materials and analytical chemistry.^26–30 Inspired by their promising properties, we herein developed a novel Ce(iv) probe based on Ce(iv)-promoted oxidation/condensation/cyclization to generate highly fluorescent benzo[a]phenazine. It is noteworthy that the Ce(iv) ion has been extensively studied as an oxidant in various chemical reactions.³¹ In this work, the Ce(iv) ion is used as a single-electron oxidant to facilitate the reaction with OPD, followed by the generation of a fluorescent product.³² In the presence of Ce(iv) ions, BNO is oxidized into naphthalene-1,2-dione and then condensed with o-phenylenediamine (OPD) to form fluorescent benzo[a]phenazine (Scheme 1). To our knowledge, this is the first detection method using the Ce(iv) ion based on the Ce(iv)-mediated cascade reaction.Open in a separate windowScheme 1Principle of the Ce(iv)-mediated cascade reaction for the detection of Ce(iv) ions.This sensing system is comprised of β-naphthol (BNO) and o-phenylenediamine (OPD). First, we investigated the fluorescence changes of a mixture of BNO and OPD in organic solvent in the presence of Ce(iv) ions. To study solvent effects, a series of organic solvents, including acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol (EtOH), and tetrahydrofuran (THF) were used. BNO (50 μM) was first mixed with Ce(iv) (120 μM), followed by adding OPD (40 μM) for 3 h at room temperature (rt). The result showed that a strong fluorescence enhancement was observed in EtOH (Fig. 1a).Open in a separate windowFig. 1Fluorescence emission spectra (E_x = 442 nm) of the sensing system containing 50 μM BNO and 40 μM OPD, with and without 120 μM Ce(iv), in the indicated organic solvents with 0.5% H₂O (a), and the emission spectra of control experiments under various conditions (b).A series of control experiments were performed to study the role of different components in this sensing system. The results showed that no fluorescence enhancement was found in the absence of any of the components (Fig. 1b). Moreover, UV-vis absorption spectra exhibited a strong absorption band between 300 nm and 400 nm, but only when all components were present (Fig. S1^†). Furthermore, when the reaction was carried out at millimolar levels in the detection system, the final product benzo[a]phenazine was obtained with structure confirmed by ¹H/¹³C NMR and melting point (Fig. S2^†). To verify the reaction mechanism, the naphthalene-1,2-dione intermediate also was isolated and characterized by NMR (Fig. S3^†). Therefore, the proposed method is capable of sensing Ce(iv) ions.Considering the importance of incubation time in a sensing system, we next investigated the change of fluorescence intensity against different incubation times. In the presence of Ce(iv) ions (120 μM), the fluorescence intensity of the system increased with longer incubation time, reaching a steady state at 3 h. In contrast, only negligible fluorescence enhancement was observed in the absence of Ce(iv) ions. Therefore, 3 h was chosen as the optimized incubation time for subsequent experiments (Fig. 2).Open in a separate windowFig. 2Fluorescence intensity of the system in the presence and absence of Ce(iv) ions over the indicated time. The concentration of BNO is 50 μM, with 40 μM OPD, and 120 μM Ce(iv) ions in EtOH containing 0.5% H₂O. The fluorescence was monitored at 15 min intervals and collected at a wavelength of 542 nm.The sensitivity of an analytical method is very important for its application. So, we examined fluorescence responses of our method to various concentrations of Ce(iv) ions. The system containing BNO (50 μM) was incubated with indicated concentrations of Ce(iv) ions at rt for 1 h and followed by adding OPD (40 μM) for 3 h. As shown in Fig. 3a, the fluorescence intensity of the system increased with the concentration of Ce(iv) (8–160 μM). Upon the addition of Ce(iv) ions, the sensor displayed more than a 200-fold fluorescence enhancement. A good linear relationship was established in a range of 16–88 μM, and the limit of detection (LOD) was calculated as 1.23 μM, according to LOD = 3σ/s.Open in a separate windowFig. 3(a) Fluorescence responses of the system to various concentrations of Ce(iv) ions. The concentration of BNO is 50 μM, with 40 μM OPD, and the concentration of Ce(iv) ions was in the range of 8–160 μM. (b) Fluorescence responses at 542 nm of the system to various concentrations of Ce(iv) ions. The inset shows the linear correlation between fluorescence intensity and the concentration of Ce(iv) ions (16–88 μM). λ_ex = 442 nm, λ_em = 542 nm.To verify the good selectivity of this method, a range of common metal ions (Al³⁺, Ba²⁺, Ag⁺, Ca²⁺, Cr³⁺, Co²⁺, K⁺, Mg²⁺, Na⁺, Fe³⁺, Mn²⁺) and rare-Earth metal ions (Dy³⁺, Gd³⁺, La³⁺, Nd³⁺, Tb³⁺, Y³⁺, Ce³⁺) were investigated. The results showed that only Ce(iv) ions triggered a significant fluorescence enhancement, and encouragingly even Ce³⁺ only slightly enhanced the fluorescence of the system (Fig. 4). However, other common and rare-Earth metal ions exhibited low fluorescence enhancement. To demonstrate the specificity of the sensor to Ce(iv) ions, a competition experiment was carried out by adding Ce(iv) ions (120 μM) to a system having the same concentration of other cations. No significant fluorescence change was observed, indicating that this reaction-based method possess great potential to detect Ce(iv) ions even in the presence of other common interfering cations. These results demonstrated high selectivity of this method towards the Ce(iv) ion, which can be attributed to the special single-electron oxidation property of the Ce(iv) ion.Open in a separate windowFig. 4Fluorescence intensity upon the addition of different metal species (Al³⁺, Ba²⁺, Ag⁺, Ca²⁺, Cr³⁺, Co²⁺, K⁺, Mg²⁺, Na⁺, Fe³⁺, Mn²⁺, Dy³⁺, Gd³⁺, La³⁺, Nd³⁺, Tb³⁺, Y³⁺, Ce³⁺, Ce(iv)). The black bars represent the addition of 120 μM concentrations of different anions to the sensing system. The red bars represent the subsequent addition of 120 μM Ce(iv) ions to the system. λ_ex = 442 nm, λ_em = 542 nm.Encouraged by the excellent sensitivity and selectivity of this sensing system, we next investigated its ability to detect Ce(iv) ions in real samples. First, a water sample from the Ganjing River (pH = 7.9) was collected and used in this work. Upon the addition of a water sample containing Ce(iv) ions (16 μM) into the sensing system, an obvious fluorescence enhancement was observed with a RSD of 0.92% (Fig. 5a). Moreover, we further explored its application to the detection of Ce(iv) ions in a lateritic soil sample collected from Ganzhou (pH = 5.4). The samples were pre-treated according to a reported method.³³ The results showed that Ce(iv) ions (24 μM) could induce a significant luminescence enhancement with a RSD of 0.93% (Fig. 5b). Taken together, we have successfully demonstrated the applicability of this sensing system to detect Ce(iv) ions in the presence of those complex matrices.Open in a separate windowFig. 5Emission spectra of the sensing system with and without Ce(iv) ions in (a) a water sample from the Ganjiang River and (b) lateritic soil samples.     

Correction: Tunnel injection from WS2 quantum dots to InGaN/GaN quantum wells

Correction for ‘Tunnel injection from WS₂ quantum dots to InGaN/GaN quantum wells’ by Svette Reina Merden Santiago et al., RSC Adv., 2018, 8, 15399–15404.

Eqn (4) in the published paper was incorrect; the correct version is shown below:4The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Homo-condensation of acetophenones toward imidazothiones

Correction for ‘Homo-condensation of acetophenones toward imidazothiones’ by Phuc Hoang Pham et al., RSC Adv., 2020, 10, 40225–40228, DOI: 10.1039/D0RA03047C.

The authors regret the omission of two references, shown below as ref. 1(a) and (b), which should have appeared as ref. 7(a) and (b).On page 40227, at the end of the paragraph which starts “With the results in hand, we proposed a possible mechanism for the annulation (Scheme 5)…” the following sentence should have been added:“It should be noted that Asinger and co-workers reported a similar transformation using ammonia, instead of ammonium acetate, that occurred in methanol solvent.¹ For that reason, an alternative mechanism should not be excluded.”The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Correction: Dipyrrolyl-bis-sulfonamide chromophore based probe for anion recognition

Correction for ‘Dipyrrolyl-bis-sulfonamide chromophore based probe for anion recognition’ by Namdev V. Ghule et al., RSC Adv., 2014, 4, 27112–27115, DOI: 10.1039/C4RA04000G.

The authors regret that an incorrect version of Fig. 1 was included in the original article. The correct version of Fig. 1 is presented below.Open in a separate windowFig. 1Color changes of receptor DPBS in chloroform upon addition of 5 equiv. of F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, HSO₄⁻, ClO₄⁻ and AcO⁻ (tetrabutylammonium salts).The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Retraction: Olefin epoxidation with chiral salen Mn(iii) immobilized on ZnPS-PVPA upon alkyldiamine

Retraction of ‘Olefin epoxidation with chiral salen Mn(iii) immobilized on ZnPS-PVPA upon alkyldiamine’ by J. Huang et al., RSC Adv., 2016, 6, 19507–19514, DOI: 10.1039/C6RA00002A.

The Royal Society of Chemistry, with the agreement of the authors, hereby wholly retracts this RSC Advances article due to extensive overlap with other published articles by these authors, including the text, data and figures published in ref. 1, which was not cited in this article. Although there are sections of original work, there are significant portions of text overlap, particularly in the Results and discussion section. Fig. 1, 3, 4 and 5, Tables 1 and 2 and Schemes 1 and 2 in the RSC Advances article have also been reproduced from ref. 1.Signed: J. Huang, D. W. Qi, J. L. Cai and X. H. ChenDate: 19^th November 2020Retraction endorsed by Laura Fisher, Executive Editor, RSC Advances